Mineral P

THE MINERAL PACHNOLITE

 

• Chemistry: NaCaAlF6 - H2O, Hydrated Sodium Calcium Aluminum Fluoride.
• Class: Halides
• Uses: As mineral specimens.
• Specimens

Pachnolite is a rare and unusual halide mineral. Chemically it is one of the most complicated halides being composed of the positive one charged (+1) sodium, the positive two charged (+2) calcium and the positive three charged (+3) aluminum. These six positive charges are countered by the six negative one charged (-1) fluorines. The symmetry of pachnolite is also unusual in that it is monoclinic, not unusual for minerals in general as many minerals are monoclinic, but unusual for halide minerals.

Pachnolite forms from the alteration of cryolite, another unusual halide mineral which by no small chance is associated with pachnolite. Pachnolite also is found with the mineral thomsenolite which has the same chemistry as pachnolite but has a slightly different structure. The better cleavage and softness of thomsenolite and its more obvious monoclinic crystal habit serve to distinguish it from pachnolite. Both minerals are found as druses lining the pockets of the very unique pegmatitic rocks at Ivigtut, Greenland.

 

PHYSICAL CHARACTERISTICS:

• Color is colorless, white or stained yellow to brown by limonite.
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent.
• Crystal System: Monoclinic.
• Crystal Habits include prismatic crystals with steep pyramidal terminations. Also pseudo-orthorhombic twinned prismatic crystals are common but tabular crystals are rare.
• Cleavage is very indistinct.
• Fracture is conchoidal.
• Hardness is 3
• Specific Gravity is 2.98 (average).
• Streak is white.
• Associated Minerals include thomsenolite, cryolite, ralstonite and limonite.
• Notable Occurrences are limited to Ivigtut, Greenland.
• Best Field Indicators are crystal habit, associations, locality and lack of good cleavage.

 

 

 

 

 

   

THE MINERAL PALYGORSKITE

 

• Chemistry: (Mg, Al)2Si4O10(OH) - 4H2O, Hydrated Magnesium Aluminum Silicate Hydroxide.
• Class: Silicates
• Subclass: Phyllosilicates
• Group: Clays
• Uses: Only as mineral specimens.
• Specimens

Palygorskite, also known as attapulgite, is an odd mineral. It forms matted felted masses that closely resemble woven cloth. In fact, an informal name for this natural fabric is "Mountain Leather" and appears with attached calcite crystals that look like interwoven glass beads.

Palygorskite is often classified as a clay mineral because it is present in some soils and behaves like many other clay minerals. Unlike most other clay minerals, palygorskite can form large crystals. Palygorskite is found in hydrothermal deposits, soils and along faults often lining the slicken sides of fault lines.

 

 

 

 

PHYSICAL CHARACTERISTICS:

• Color is white, gray pale lavender.
• Luster is silky to dull.
• Transparency: Crystals are transparent to translucent.
• Crystal System is monoclinic; 2/m
• Crystal Habits include fibrous felted masses termed "Mountain Leather" as well as disseminated grains and platy crystals.
• Cleavage is perfect in one direction producing thin sheets or flakes.
• Fracture is not readily observed due to cleavage, but is uneven.
• Hardness is less than 2.
• Specific Gravity is approximately 2.2+ (well below average)
• Streak is white.
• Other Characteristics: Thin crystal sheets are flexible.
• Associated Minerals include calcite, clays and serpentine.
• Notable Occurrences include Pend Oreille Mine, Metaline Falls, Washington (good "Mountain Leather" source) and Arizona, USA; Morocco; Molotov Mining District of the Ural Mountains in Russia and the Shetland Islands.
• Best Field Indicators are crystal habit, flexible sheets, environments and associations.

 

 

   

THE MINERAL PAPAGOITE

 

• Chemistry: CaCuAlSi₂O₆(OH)₃; Calcium Copper Aluminum Silicate Hydroxide
• Class: Silicates
• Subclass: Cyclosilicates
• Uses: Only as a mineral specimen
• Specimens

Papagoite is another rare copper silicate from the mines of Arizona, USA. It is found at only one mine in Arizona, the New Cornelia Mine, Ajo District in Pima County. The only other world-wide location is at Messina, Transvaal, South Africa. The Arizona mine is the type locality. Papagoite is one of only a few four membered ring silicates. These silicates have four silicate tetrahedrons linked into a ring forming a distorted square-like structural element. Papagoite is named for the Papago Indian tribe of Arizona. It forms as a secondary mineral on slip surfaces and in veins in altered granodiorites.

 

PHYSICAL CHARACTERISTICS:

• Color is a dark sky blue in crystals and a paler blue in massive veins.
• Luster is vitreous to dull.
• Transparency: crystals are translucent.
• Crystal System is monoclinic; 2/m.
• Crystal Habits include tiny flattened, elongated crystals sometimes formed into spherical aggregates and massive vein filling material.
• Cleavage is imperfect in one direction.
• Hardness is 5 - 5.5
• Specific Gravity is approximately 3.3 (slightly above average for non-metallic minerals)
• Streak is pale blue.
• Associated Minerals are limited to aurichalcite, ajoite, barite, shattuckite and limonite.
• Notable Occurrences include the New Cornelia Mine, Ajo District in Pima County, Arizona, USA and Messina, Transvaal, South Africa.
• Best Field Indicators are crystal habit, associations, color and locality.

 

 

 

 

THE MINERAL PARADAMITE

 

• Chemistry: Zn2AsO4(OH), Zinc Arsenate Hydroxide
• Class: Phosphate Class
• Subclass: Arsenates
• Uses: Only as mineral specimens
• Specimens

Paradamite is dimorphous with a famous arsenic mineral, namely adamite. Dimorphous means that the two minerals have the same formula, but different structures (di means two; morphous means shape). Paradamite's different structure produces only slight differences in physical properties. Most obvious however is the difference in crystal forms. Adamite's typical form is wedge shaped prismatic crystals with diamond-shaped cross-sections. Paradamite's form is more tabular in character and very different from adamite's. Although their names are similar and their chemistry is the same; paradamite and adamite are absolutely distinct minerals.

Curiously, paradamite is associated with adamite as well as other common oxidized arsenic minerals. It is curious because often dimorphic minerals are not directly associated. The diverse conditions required to produce a different structure from the same chemistry are often so radically different that the minerals are not found together. However if the conditions required to produce the two minerals are only slightly different; then the two minerals can be found together and sometimes grade into each other. What those exact conditions are, and how much they must change to produce the dimorph is of great interest to mineralogists and petrologists.

 

PHYSICAL CHARACTERISTICS:

• Color is pale yellow
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent.
• Crystal System is triclinic; bar 1.
• Crystal Habits include rounded tabular crystals, usually aggregated.
• Cleavage is perfect.
• Fracture is uneven.
• Hardness is 3.5.
• Specific Gravity is approximately 4.5 - 4.6 (heavy for translucent minerals)
• Streak is white.
• Other Characteristics: Some specimens are fluorescent yellow (adamite usually fluoreses green) under shortwave UV light.
• Associated Minerals include adamite, legrandite, limonite, smithsonite, austinite, mimetite and other zinc oxidation zone minerals.
• Notable Occurrence is limited to the famous mines of Mapimi, Durango, Mexico.
• Best Field Indicators are crystal habit, color, density, fluorescence and associations.

 

THE MINERAL PARASYMPLESITE

 

• Chemistry: Fe3(AsO4)2 - 8H2O, Hydrated Iron Arsenate
• Class: PhosphateClass
• Subclass: Arsenates
• Group: Vivianite
• Uses: Only as mineral specimens.
• Specimens

Parasymplesite is a rare iron arsenate mineral that can make nice micromounted specimens. It can form spherical aggregates of acicular crystals with a green color. It is dimorphous with the mineral symplesite, hence its name. Both minerals have the same exact chemistry, but they have different structures resulting in different symmetries. Parasymplesite is monoclinic while symplesite is triclinic.

Parasymplesite is also in a solid solution series with the mineral kottigite. A solid solution series exists when two or more elements can fill the same position within the structure of two or more minerals. In this case, iron and zinc can occupy the same position in the kottigite/parasymplesite structure. Kottigite is the zinc rich member of the series and parasymplesite is the iron rich member. Parasymplesite and kottigite are isostructural (meaning same structure) with all members of the Vivianite Group of minerals. However, not all of them share elements within their structures.

 

PHYSICAL CHARACTERISTICS:

• Color is greenish blue, greenish gray or green.
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent.
• Crystal System is monoclinic.
• Crystal Habits include tabular or acicular crystals, radiating fibrous and massive crusts.
• Cleavage is perfect.
• Fracture is uneven.
• Hardness is 2
• Specific Gravity is approximately 3.0 - 3.1 (average for translucent minerals).
• Streak is white.
• Associated Minerals are kottigite, pyrite and symplesite
• Notable Occurrences include Alsace, France and Japan.
• Best Field Indicators are color, crystal habit, cleavage, softness and associations.
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 THE MINERAL PARAVAUXITE

 

• Chemistry: FeAl2(PO4)2(OH)2 - 8H2O, Hydrated Iron Aluminum Phosphate Hydroxide.
• Class: Phosphates
• Group: Paravauxite.
• Uses: Only as mineral specimens.
• Specimens

Paravauxite is closely related to its basic namesake vauxite. Paravauxite appears to be different from vauxite only in the number of water molecules in the structure. Paravauxite has eight water molecules while vauxite has only six in its formula. It is the presence of these water molecules that alters the structure to the point that paravauxite has perfect cleavage while in sharp contrast, vauxite has no cleavage at all. Cleavage is one property that is undeniably tied to the structure of a mineral. The only other strikingly different property is paravauxite's green to colorless color verses vauxite's blue color.

Metavauxite is another closely named and closely related mineral to paravauxite. It is a dimorph of paravauxite. A dimorph is a mineral that has the same chemistry, but a different structure. In this case, the structure of paravauxite is triclinic while the structure of metavauxite is monoclinic in symmetry. Although one might think so, vauxite and paravauxite are not dimorphs since they share neither the same structure (although both are triclinic) nor the same chemistry (thanks to those water molecules). Vauxite, paravauxite and metavauxite are all found at the famous tin oxide deposits at Llallagua, Potosi, Bolivia. All are associated with the primary tin ore, cassiterite. They form as a result of precipitation from hydrothermal solutions.

Paravauxite is the name of a somewhat rare phosphate mineral and an obscure mineral group. The Paravauxite Group is composed of other triclinic phosphates that have the following general formula:

XY2(PO4)2(OH)2 - 8H2O

or XY2(PO4)2(OH)3 - 7H2O

The X ion can be either iron(+2), magnesium, manganese or iron(+3) while the Y ion can be either aluminum, iron(+3) or to a lesser extent, chromium. The second formula is used when the X ion is the iron(+3) in stead of the iron(+2) and the additional positive charge requires the additional hydroxide and one less water molecule.

These are the members of the Paravauxite Group with their respective formula:

• Gordonite MgAl2(PO4)2(OH)2 - 8H2O
• Laueite MnAl2(PO4)2(OH)2 - 8H2O
• Paravauxite FeAl2(PO4)2(OH)2 - 8H2O
• Sigloite FeAl2(PO4)2(OH)3 - 7H2O
• Ushkovite MgFe2(PO4)2(OH)2 - 8H2O

 

 

 

THE PHYSICAL CHARACTERISTICS OF PARAVAUXITE:

• Color is colorless, white or pale green.
• Luster is vitreous to pearly.
• Transparency: Specimens are translucent to transparent.
• Crystal System is triclinic.
• Crystal Habits include tabular crystals and radiating fibrous masses.
• Cleavage is perfect.
• Fracture is conchoidal.
• Hardness is 3
• Specific Gravity is approximately 2.4 (average).
• Streak is white.
• Associated Minerals include cassiterite, metavauxite, vauxite, wavellite, quartz and limonite.
• Notable Occurrences are limited to the famous tin deposits at Llallagua, Potosi, Bolivia and a few minor localities around the world.
• Best Field Indicators are color, locality, crystal habit, associations and perfect cleavage.

 

  

 THE MINERAL PARISITE

 

• Chemistry: Ca(Ce, La, Nd)2(CO3)3F2 , Calcium Cerium Lanthanum Neodymium Carbonate Fluoride.
• Class: Carbonates
• Groups: Rare earth carbonates and Bastnasite.
• Uses: As a minor ore of cerium and other rare earth metals and as mineral specimens.
• Specimens

Parisite, which is named for the owner of the mine (J.J. Paris) at which parisite was discovered, is one of a few rare earth carbonate minerals. Some of the other more common rare earth carbonates are ancylite, carbocernaite, tengerite, lanthanite, synchysite, ewaldite, burbankite, donnayite and bastnasite. Parisite has cerium, neodymium and lanthanum in its generalized formula but officially the mineral is divided into two minerals based on the respective predominant rare earth element. There is the more common parisite-(Ce) with a more accurate formula of Ca(Ce, La)2(CO3)3F2. And there is the rarer parisite-(Nd) with a formula of Ca(Nd, Ce, La)2(CO3)3F2. There is little difference in the two in terms of physical properties and most Parisite is actually Parisite-(Ce).

Parisite is closely related to three other distinct minerals; synchysite, bastnasite and rontgenite-(Ce) The four are all Bastnasite Group minerals of similar formulas and occurrence. In Fact the four are often intergrown and a single crystal of any of these minerals probably contains at least one of the other minerals and possibly all four. As expected they can be difficult to distinguish from one another. One unique method involves the dissolvability of the four minerals in acids. Bastnasite is nearly indissolvable in cold nitric acid followed by parisite's slow dissolution, while rontgenite readily dissolves and synchysite dissolves the quickest. With a practiced hand, identification of samples can be made by gauging the rates of dissolution. Differing dissolution rates within a single crystal can also confirm the multiple phases or species that exist within the crystal, but this also tends to ruin the specimen. The zoning of different phases is not generally visible in untested specimens. Crystals often will show a zoning of inclusions but these do not indicate the boundaries of phases.

Parisite is only found as small crystals and can be used for micromounts. Some crystals have been reported to have been cut as gems, but normally the crystals of parisite are too small and cloudy to make good gemstones. Parisite crystals are found in carbonatites, granite pegmatites and alkaline syenites and the hydrothermal deposits associated with them. Parisite is a significant ore at the bastnasite mines of Mountain Pass, California.

 

PHYSICAL CHARACTERISTICS:

• Color is white, tan, yellow-brown, reddish-brown, brown, yellow and pale pink.
• Luster is vitreous, resinous to dull.
• Transparency: Crystals are translucent to more rarely transparent.
• Crystal System is trigonal.
• Crystal Habits include small acicular, platy or thin tabular crystals that form rosettes. Also known to form double hexagonal pyramids and rhombohedrons. Often intergrown in a lamellar fashion with synchysite, rontgenite and bastnasite.
• Cleavage is fair to good in one direction (basal).
• Fracture is subconchoidal to splintery.
• Hardness is typically around 4.5 but will vary from 4 to 5.
• Specific Gravity is approximately 4.2 to 4.3 (well above average)
• Streak is white to yellowish white.
• Other Characteristics: Only slightly soluble in nitric acid, a strong basal parting is also sometimes seen and crystals are typically striated parallel to the basal face.
• Associated Minerals are extensive and include bastnasite, rontgenite-(Ce), synchysite, gold, fluorite, sahamalite-(Ce), dolomite, barite, allanite, aegirine, calcite, ancylite, albite, pectolite, microcline, riebeckite, cerite, rhodochrosite, sphene, ankerite, biotite, monazite and xenotime.
• Notable Occurrences include the type locality in the Muzo emerald deposit in the Muzo district, Bogota, Colombia. Other localities include the Mountain Pass, San Bernardino, California; Quincy, Mass.; Mohave County, Arizona and Mineral and Ravelli Counties, Montana, USA; Narsarsuk, Greenland; the mines of Mont Saint-Hilaire, St. Honore and Gatineau, Quebec and the Thor Lake deposits, Northwest Territories, Canada; langesundsfjord area, Norway and the Weishan deposit, Weishan Lake district, Shandong Province, China and the type locality for parisite-(Nd) that being Bayan Obo, inner Mongolia, China.
• Best Field Indicators: crystal habit, color, cleavage, density, luster, low solubility in nitric acid and locality.

 

 

 

 

 

   

THE MINERAL PECTOLITE

 

• Chemistry: NaCa2Si3O8(OH), Sodium Calcium Silicate Hydroxide
• Class: Silicates
• Subclass: Inosilicates
• Group: Pyroxenoid
• Uses: mineral specimens and as a semi-precious stone.
• Specimens

Also see variety specimens:

• Lorimar Specimens

Pectolite is a mineral that can be confused with several other similar appearing minerals. These include okenite, wollastonite, artinite and a few others. Fortunately, most of these minerals do not form with zeolites as pectolite is so apt to do. Okenite is one of those that does, but is soft and bendable, unlike pectolite.

Pectolite is a nice specimen type mineral, meaning that it can form interesting specimens from time to time. However it was not all that well-regarded until a variety was discovered in the Bahamas and the Dominican Republic. It has been given the trade name Lorimar and has enjoyed success in the semi-precious stone market.

 

PHYSICAL CHARACTERISTICS:

• Color is white, colorless or gray and also pale to sky blue in Lorimar.
• Luster is vitreous to silky.
• Transparency: Crystals are transparent to translucent.
• Crystal System is triclinic; bar 1
• Crystal Habits include fibrous tufts, radiating acicular crystal clusters and compact or botryoidal masses.
• Cleavage is perfect in two direction at close to right angles.
• Fracture is splintery due to the cleavage.
• Hardness is 4.5 - 5
• Specific Gravity is approximately 2.7 - 2.9 (average)
• Streak is white.
• Associated Minerals are various zeolites, prehnite, calcite, datolite and serpentine.
• Other Characteristics: Splinters of pectolite do not bend and are brittle. They are also sharp and can easily puncture the skin if not handled properly. Also some specimens can be triboluminescent.
• Notable Occurrences include Lake Co., California and Paterson and Franklin, New Jersey, USA; Bahamas, Dominican Republic; Italy and England.
• Best Field Indicators are crystal habit, association with zeolites, brittleness and cleavage.

 

THE MINERAL PENTLANDITE

 

• Chemistry: (Fe, Ni)9S8, Iron Nickel Sulfide.
• Class: Sulfides
• Group: Pentlandite
• Uses: As the principle ore of nickel, a minor ore of iron and as mineral specimens.
• Specimens

Pentlandite is an important ore of nickel. However, it does not produce good crystals and is generally only found in massive form. It is commonly associated with other sulfides such as pyrite, chalcopyrite and pyrrhotite in basic igneous rock intrusions. These sulfide ore bodies are probably produced through magmatic segregation. As the hot liquid of the magma cools, crystals of high-density minerals such as metal sulfides fall to the bottom of the magma chamber and collect into one large metal-rich bonanza for mining companies.

Pentlandite's close association with the mineral pyrrhotite (Fe_1-xS) is believed to be the result of exsolution that occurs after magmatic segregation. At higher temperatures and pressures, the chemicals that make up the two minerals are compatible in a more or less semi-solid form. But as the temperature and pressure lower, the two chemistries become incompatible and they separate into two different minerals. The two are difficult to differentiate when pyrrhotite is in a massive form. Both are brassy yellow, dense and metallic with a hardness around 4 and a similar streak. Pyrrhotite is usually magnetic, although weakly so, and lacks the octahedral parting of pentlandite which provides the only good field tests for differentiation. But the two are so often and intimately associated that if you have a sample of pentlandite, you can be assured that you also have pyrrhotite!

Pentlandite's formula is believed to be composed of equal amounts of nickel and iron, but does show variation in tests, probably as a result of pyrrhotite inclusions in test samples. The structure of pentlandite is rather complex, with a face centered cubic arrangement and the metal ions in tetrahedral and octahedral coordination with the sulfurs. Coordination refers to the number and position of the sulfurs surrounding the metal ions. In the case of tetrahedral coordination, there are four sulfurs surrounding one metal ion and they are positioned at the four points of a tetrahedron. In the case of octahedral coordination, there are six sulfurs at the six points of an octahedron with a metal ion inside.

Pentlandite lends its name and structure to a group of minerals called the Pentlandite Group. It is a group of rather rare minerals, save for pentlandite, that all have the same structure and somewhat similar chemistries. The general formula is AB8(S, Se)8 where silver, manganese, cadmium or lead can be found in the A position. While the B position can be occupied by copper. More versatile metals such as iron, nickel and cobalt can occupy either the A or B positions.

These are the members of the Pentlandite Group:

• Argentopentlandite (Silver Iron Nickel Sulfide)
• Cobalt pentlandite (Cobalt Iron Nickel Sulfide)
• Geffroyite (Copper Iron Silver Lead Selenide Sulfide)
• Manganese-shadlunite (Iron Copper Manganese Lead Sulfide)
• Pentlandite (Iron Nickel Sulfide)
• Shadlunite (Iron Copper Lead Cadmium Sulfide)

 

PHYSICAL CHARACTERISTICS OF PENTLANDITE:

• Color is muted brassy to bronze yellow.
• Luster is metallic.
• Transparency crystals are opaque.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits are limited to mostly massive rock forming formations and as granular components of massive sulfide rocks.
• Hardness is 3.5 - 4
• Specific Gravity is approximately 4.6 - 5.0 (average for metallic minerals)
• Streak is light brown to light bronze.
• Other Characteristics: Octahedral parting is generally evident as odd cracks or fractures in the massive material and the lack of any magnetism helps differentiate it from the similar and often associated pyrrhotite.
• Associated Minerals include pyrrhotite, niccolite, biotite, millerite, pyrite and chalcopyrite
• Notable Occurrences include a large deposit at Sudbury, Ontario and smaller deposits at Lynn Lake and Moak Lake, Manitoba and Malartic, Quebec, Canada; Ducktown, Tennessee and San Diego County, California, USA; Russia; Bushveld, Transvaal, South Africa and Lillehammer, Norway.
• Best Field Indicators are parting, associations, lack of magnetism, streak and color.

 

THE MINERAL PERICLASE

 

• Chemical Formula: MgO, Magnesium Oxide
• Class: Oxides and Hydroxides
• Uses: As mineral specimens and sometimes as gemstones.
• Specimens

Periclase is sometimes used as a gemstone although it lacks good hardness and is generally limited in colors. Periclase is isostructural with halite, NaCl, which has simple cubic packing and produces cubic and octahedral crystals. Periclase is relatively scarce and is found in marbles being formed from the dissolution of dolomite, CaMg(CO3)2 , into MgO-periclase, CaCO3-calcite and CO2-carbon dioxide. This dissolution takes place during metamorphism. If the periclase rich marbles are exposed to weathering the periclase easily alters to either brucite, Mg(OH)2 or hydromagnesite, Mg5(CO3)4(OH)2 - 4H2O. The yellow brown and black colors of periclase are due to the presence of iron. Specimens of periclase can be very attractive as brightly lustered, smoothly faceted crystals projecting out of the otherwise formless rough marble host rock.

 

PHYSICAL CHARACTERISTICS:

• Color is colorless, white, gray, yellow to brown or black
• Luster is vitreous to adamantine.
• Transparency crystals are transparent to translucent.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits include the typical cubes and octahedrons as well as rounded indistinct grains.
• Cleavage is perfect in three directions forming cubes.
• Hardness is 5.5
• Specific Gravity is 3.6 (slightly above average)
• Streak is white.
• Other Characteristics: Crystals may dull in humid air.
• Associated Minerals include brucite, dolomite, hydromagnesite, magnesite, spinel, chondrodite and forsterite.
• Notable Occurrences include Monte Somma, Vesuvius, Italy; Crestmore, California, USA and Nordmark, Varmland, Sweden.
• Best Field Indicators are crystal habit, luster, hardness, cleavage, associations and localities.

 

 

PERIDOT,

the gemstone variety of olivine

 

VARIETY INFORMATION:

• VARIETY OF: Olivine , (Mg, Fe)₂SiO₄.
• USES: gemstone.
• BIRTHSTONE FOR: August
• COLOR: shades of green usually from yellow-green to greenish yellow.
• INDEX OF REFRACTION: 1.630 - 1.695
• BIREFRINGENCE: 0.037
• HARDNESS: 6.5 - 7
• CLEAVAGE: usually not discernible
• CRYSTAL SYSTEM: orthorhombic
• For natural peridot mineral specimens see our For Sale or Sold lists

Peridot (pronounced pair-a-doe) is the gem variety of olivine. Olivine, which is actually not an official mineral, is composed of two minerals: fayalite and forsterite. Fayalite is the iron rich member with a pure formula of Fe₂SiO₄. Forsterite is the magnesium rich member with a pure formula of Mg₂SiO₄. Olivine's formula is written as (Mg, Fe)₂SiO₄ to show the substitution of the magnesium and iron. Peridot is usually closer to forsterite than fayalite in composition although iron is the coloring agent for peridot. The best colored peridot has an iron percentage of less than 15% and includes nickel and chromium as trace elements that may also contribute to the best peridot color.

Gem quality peridot comes from the ancient source of Zagbargad (Zebirget) Island in the Red Sea off the coast of Egypt; Mogok, Myanmar (formerly known as Burma); Kohistan, Pakistan; Minas Gerais, Brazil; Eifel, Germany; Chihuahua, Mexico; Ethiopia; Australia; Peridot Mesa, San Carlos Apache Reservation, Gila County, Arizona and Salt Lake Crater, Oahu, Hawaii, USA. The best quality peridot has historically come either from Myanmar or Egypt. But new sources in Pakistan are challenging that claim with some exceptional specimens. The Arizona gem material is of lesser quality, but is far more abundant and is therefore much more affordable. An estimated 80 - 95% of all world production of peridot comes from Arizona. The Myanmar, Pakistani and Egyptian gems are rarer and of better quality and thus quite valuable approaching the per carat values of top gemstones. Possibly the most unusual peridot is that which comes from iron-nickel meteorites called pallasites. Some are actually facetted and set in jewelry.

Peridot is perhaps derived from the French word peritot which means unclear, probably due to the inclusions and cloudy nature of large stones. It could also be named from the Arabic word faridat which means gem. In either case, peridot has been mined as a gemstone for an estimated four thousand years or better, and is mentioned in the Bible under the Hebrew name of pitdah. Peridot gems along with other gems were probably used in the fabled Breastplates of the Jewish High Priest, artifacts that have never been found. The Greeks and Romans referred to peridot as topazion and topazius respectively and this name was later given to topaz, to end the confusion with the two gems. Historical legend has it that peridot was the favorite gemstone of Cleopatra. Pliny wrote about the green stone from Zagbargad Island in 1500 B.C.. Even until recently have jewelers used the term "chrysolite" (latin for golden stone) in referring to peridot gems for some reason. This term has also been used to refer to other gemstones, of a more golden color.

Zagbargad (Zebirget) Island has been known as St John's Island and was mined for centuries. Before World War I, this island was extensively mined and produced millions of dollars worth of gems. Since then the mining has been off and on and at present is all but nonexistent. Still, specimens from here are available at times and it certainly is a classic mineral locality.

Throughout time, peridot has been confused with many other gemstones, even emerald. Many "emeralds" of royal treasures have turned out to be peridots! And although peridot is distinctly a different shade of green, many jewelers refer to peridot as "evening emerald". Emerald is a dark green as opposed to a yellow green and always contains inclusions. Other green gemstones confused with peridot include apatite (which is much softer); green garnets (have no double refraction), green tourmaline and green sinhalite (both of which are strongly pleochroic), moldavites (no double refraction) and green zircon (significantly heavier). All of these gemstones rarely have as nice a yellow component to their green color as does most peridot, but darker green peridot can be confusing when good crystal form is not discernible.

Peridot is a beautiful gemstone in its own right and is widely popular. Its popularity is said to be increasing yearly and with new finds in Pakistan producing exceptionally well crystallized specimens, peridot can be fun to collect for years to come.

 

   

THE MINERAL PEROVSKITE

 

• Chemical Formula: CaTiO3, Calcium Titanium Oxide
• Class: Oxides and Hydroxides
• Group: Perovskite
• Uses: A minor ore of titanium and rare earth metals and as mineral specimens.
• Specimens

Perovskite is an increasingly economically important, and in some rocks a rather common, mineral. It is sought after for its rare earth metal content. Often perovskite is enriched in cerium, niobium, thorium, lanthanum, neodymium and other rare earth metals. Rare earth metals are becoming rather attractive for prospectors due to their growing value to industry. The titanium derived from perovskite is recovered as well.

Crystals of perovskite appear as cubes, but this is deceiving. Perovskite is actually pseudocubic (or "falsely shaped" in a loose translation from the Greek). It is really orthorhombic in symmetry, but its structure is very close to isometric. The titaniums and oxygens compose a framework structure in which TiO6 octahedrons are connected at each corner to other TiO6 octahedrons. If the connections were at perfect 90 degree angles then the structure would be isometric.

However the large ions, such as calcium and some rare earth metals that are needed to balance the formula, are too large to fit comfortably between the octahedrons. This causes a bending or twisting of the octahedrons and a distortion of the structure to orthorhombic symmetry. But the structure is still close to being isometric and it can therefore create crystals that are close to being cubes. Specimens can remind one of darkly colored cubes of galena. But galena's better metallic luster, greater density and perfect cleavage will give nobody any trouble in permanently confusing the two.

Perovskite is named for a Russian mineralogist, Count Lev Aleksevich von Perovski. The mineral was discovered and named by Gustav Rose in 1839 from samples found in the Ural Mountains. Now it is a well known and recognized as a common mineral in aluminum and silica poor rock types such as nepheline syenites, carbonatites, kimberlites and melilites as well as some contact metamorphic marbles.

 

PHYSICAL CHARACTERISTICS:

• Color is variable from black, brown, gray, orange to yellow.
• Luster is submetallic to adamantine, greasy or waxy.
• Transparency: Crystals are opaque.
• Crystal System is Orthorhombic (pseudocubic).
• Crystal Habits include commonly pseudocubic striated crystals. Also found bladed, reniform, granular and massive.
• Cleavage is imperfect in one direction.
• Fracture is conchoidal.
• Hardness is 5.5
• Specific Gravity is 4.0 (below average for metallic minerals)
• Streak is white to gray.
• Associated Minerals include chlorite, talc, serpentine, melilite, andradite, nepheline, sphene and leucite.
• Notable Occurrences include the Slatoust district, Ural Mountains, Russia; Sweden; Crestmore Quarries, Riverside County and the Diablo Range, San Benito County, California; the Bearpaw Mountains, Montana and Magnet Cove Arkansas, USA; Zermatt, Switzerland; Gardiner complex, Greenland; Jacupiranga, Sao Paulo, Brazil; Val Malenco, Lombardy, Italy and the Eifel District, Germany.
• Best Field Indicators are crystal habit, luster, associations, striations and locality.

 

 

 

THE MINERAL PHARMACOLITE

 

• Chemistry: Ca(AsO3OH)-2H2O, Hydrated Calcium Arsenate Hydroxide.
• Class: Phosphates
• Subclass: Arsenates
• Uses: Only as mineral specimens.
• Specimens

Pharmacolite is a rather rare arsenic mineral. It is named from the Greek word for poison in allusion to its arsenic content. Ironically it is the same word that gives us pharmacy. There are a couple of other arsenate minerals that have similar names to pharmacolite, namely pharmacosiderite and picropharmacolite. Despite having similar names and being arsenic mineral they are otherwise unrelated.

Pharmacolite is related to a few minerals that have a similar formula and structure. Of these only gypsum is common.

• Gypsum CaSO4) - 2H2O
• Ardealite Ca2(PO3OH)(SO4) - 4H2O
• Brushite. Ca(PO3OH) - 2H2O

 

PHYSICAL CHARACTERISTICS:

• Color is white, colorless or gray.
• Luster is vitreous to pearly.
• Transparency: Specimens are translucent to transparent.
• Crystal System is monoclinic.
• Crystal Habits include acicular crystals and botryoidal crusts and masses.
• Cleavage is perfect.
• Hardness is 2 - 2.5
• Specific Gravity is approximately 2.7 (average).
• Streak is white.
• Associated Minerals include erythrite and other secondary oxidation minerals.
• Notable Occurrences include Wittichen, Schwarzwald, Germany; Ste. Marie-aux-Mines, Alsace, France and San Gabriel Canyon, California, USA.
• Best Field Indicators: color, crystal habit, locality and associations.

 

   

THE MINERAL PHENAKITE

 

• Chemistry: Be2SiO4, Beryllium silicate.
• Class: Silicates
• Subclass: Nesosilicates
• Group: Phenakite
• Uses: sometimes cut as a gemstone and as mineral specimens.
• Specimens

Phenakite is a rare beryllium mineral, but it is found so frequently with precious gemstones that its availablity is not in proportion to its rarity. It is found in pegmatitic pockets and is associated with gemstones such as topaz, beryl especially emerald, chrysoberyl and smoky quartz. The name phenakite, or the alternate spelling, phenacite, is from a Greek word meaning deceiver, an allusion to its deceptively similar look to quartz.

Phenakite is one of the few silicate minerals that have a trigonal symmetry. This symmetry is far more common among carbonates than among silicates. Phenakite shares the same symmetry with the emerald green silicate dioptase and the fluorescent and closely related willemite.

Fine crystals of phenakite can be perfectly clear and with good hardness, rarity and lack of good cleavage, although somewhat lacking in color and fire, make good choices for gemstones.

 

PHYSICAL CHARACTERISTICS:

• Color is usually colorless or white but can be tinted yellow, brown and pink.
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System: trigonal; bar 3
• Crystal Habits include flatten rhombohedral to almost tabular and typically short prismatic crystals although some prismatic crystals can be rather long. Also lenticular. Twinning is common and forms penetration twins
• Cleavage in poor in three directions.
• Fracture is conchoidal.
• Hardness is 7.5 - 8
• Specific Gravity is approximately 2.9 - 3.0 (average for non-metallic minerals).
• Streak is white.
• Other Characteristics: Prism faces striated lengthwise and index of refraction is approximately 1.66.
• Associated Minerals are topaz, cassiterite, quartz, calcite, hematite, feldspars, apatite, fluorite, beryl especially emerald, chrysoberyl, bertrandite and some sulfides.
• Notable Occurrences include sites on the Takowaja River, Ural Mountains, Russia; Minas Gerias, Brazil; Pala, San Diego Co., California; Mt. Antero and Pikes Peak, Colorado, USA and Norway.
• Best Field Indicators are crystal habit, striations, enviroment and hardness.
•  

 

 

THE MINERAL PHILLIPSITE

 

• Chemistry: KCaAl3Si5O16 - 6H2O, Hydrated potassium calcium aluminum silicate.
• Class: Silicates
• Subclass: Tektosilicates
• Group: Zeolites
• Uses: Mineral specimen and chemical filter.
• Specimens

Phillipsite is one of the rarer zeolites, but is popular among zeolite collectors. It forms interesting aggregates that are commonly clustered into bright white sphericules or balls with a rough crystalline or silky surface. Phillipsite is known to occur as an encrusting precipitate around hot springs. However, phillipsite is more commonly found in the vesicles or bubbles of volcanic rock as are most other zeolites.

Zeolites have an openness about their structure that allows large ions and molecules to reside and actually move around inside the overall framework. The structure actually contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like phillipsite can act as a chemical sieve, allowing some ions to pass through while blocking others.

 

PHYSICAL CHARACTERISTICS:

• Color is clear, white, yellowish and reddish.
• Luster is vitreous, also silky on sphericule's surfaces.
• Transparency: Crystals are transparent to translucent.
• Crystal System is monoclinic; 2/m
• Crystal Habits include attached crystal aggregates. Single tabular crystals are rare, more commonly twinned into "fourlings" or more complicated groupings. Sphericules are small tight balls that have a sparkling or silky luster in phillipsite. Aggregates can be radiating, fibrous, columnar and encrusting.
• Cleavage is imperfect in one direction.
• Fracture is uneven.
• Hardness is 4 - 4.5.
• Specific Gravity is approximately 2.2 (very light)
• Streak is white.
• Associated Minerals are quartz, calcite, chabazite, natrolite, heulandite, stilbite and other zeolites.
• Notable Occurrences include Siegerland, Germany; Moyle, Northern Ireland; Capo di Bove and Mt. Vesuvius, Italy; Groschlattengruen, Bavaria; Cape Grim, Tasmania, Australia and Iceland.
• Best Field Indicators are crystal habit, twinning, density, hardness and associations.

 

 

THE MINERAL PHLOGOPITE

 

• Chemistry: K Mg3 AlSi3 O10 (OH)2, Potassium magnesium aluminum silicate hydroxide.
• Class: Silicates
• Subclass: Phyllosilicates
• Group: Micas
• Uses: heat and electrical insulator for industrial purposes.
• Specimens

Phlogopite is a rarer member of the mica group and is not well known even by mineral collectors. It has been mined however for its heat and electrical insulating properties which are considered superior to other micas. The typical light brown color of phlogopite is characteristic although it is difficult to distinguish brown biotite from dark brown phlogopite. The two are actually end members in a series that is dependent on the percentage of iron. Phlogopite is iron poor and biotite is iron rich. The darker color and density increase with an increase in the iron content. Biotite tends to form in a wider range of conditions than phlogopite which is limited mostly to ultramafic rocks and magnesium rich marbles and pegmatites.

Phlogopite, like other micas, has a layered structure of magnesium aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Phlogopite is rarely considered a valuable mineral specimen, but well formed crystals are rare and some are now on the market showing nice crystals. These come from the Kola Pennisula area of Russia. Single large plates or "books" of phlogopite can grow to considerable size.

 

PHYSICAL CHARACTERISTICS:

• Color is pale brown to brown.
• Luster is vitreous to pearly.
• Transparency crystals are transparent to translucent.
• Crystal System is monoclinic; 2/m
• Crystal Habits include tabular to prismatic crystals with a prominant pinacoid termination. Phlogopite's four prism faces and two pinacoid faces form pseudo-hexagonal crystal "books". The sides of the crystal often tend to tapper and can have a "hard candy that has been sucked on, look". Also as lamellar or granular rock forming masses.
• Cleavage is perfect in one direction producing thin sheets or flakes.
• Fracture is not readily observed due to cleavage but is uneven.
• Hardness is 2.5 - 3.
• Specific Gravity is approximately 2.9+ (average)
• Streak is white.
• Associated Minerals are dolomitic marbles, hornblende, garnets and schorl.
• Other Characteristics: cleavage sheets are flexible and elastic, meaning they can be bent and will flex back to original shape. Thin flakes show an asterism or six rayed star when a light source is viewed through the crystal due to inclusions.
• Notable Occurrences include Ontario and Quebec, Canada; Russia and at many locallities in Europe.
• Best Field Indicators are crystal habit, color, cleavage, elastic sheets and associations.

 

THE MINERAL PHOSGENITE

 

• Chemistry: Pb2CO3Cl2, Lead Carbonate Chloride
• Class: Carbonate
• Uses: Only as mineral specimens.
• Specimens

Phosgenite is a relatively rare mineral and has a rare symmetry, tetragonal, for a carbonate mineral. It has a high luster due to its lead content, just as glass crystal sparkles more when its lead content increases. Phosgenite also fluoresces bright yellow under UV light, adding to its desirability as a collection piece. Phosgenite forms from the oxidation of lead bearing minerals such as when galena comes in contact with carbonated and chlorinated waters. As an interesting footnote, phosgenite has been found in the Mediterranean Sea's slag dumps of the ancient greeks. The lead rich rocks have reacted with the sea water over time forming phosgenite crystals.

 

PHYSICAL CHARACTERISTICS:

• Color is colorless, white, brown to yellow
• Luster is adamantine to greasy.
• Transparency: Crystals are transparent to translucent.
• Crystal System is tetragonal; 4 2 2
• Crystal Habits: Generally crystals are long slender prismatic to acicular with either a pinacoidal, a tetragonal trapezohedral or a pyramidal termination that tappers due to multiple secondary pyramidal faces. Can also be stubby, tabular, massive and granular. Large crystals (some up to half a foot long) are weakly striated lengthwise.
• Hardness is 2.+ - 3.0; a fingernail (hardness 2.5) will scratch a prism face parallel to the long axis, but not across it.
• Specific Gravity is 6.0+ (very heavy for translucent minerals)
• Cleavage is good in two directions lengthwise (prismatic), poor basal cleavage
• Fracture is conchoidal.
• Streak is white.
• Associated Minerals include cerussite, anglesite, galena and limonite.
• Other Characteristics: Usually exhibits a bright yellow fluorescence in ultraviolet light.
• Notable Occurrences include Tsumeb, Namibia; Sardinia, Italy; Tiger Mine, Arizona, Inyo Co., California and Colorado, USA; Matlock, England and Laurium, Greece.
• Best Field Indicators are fluorescence, density, variable hardness, color, crystal habit and high luster.

 

 

 

 

 

THE MINERAL PHOSPHOPHYLLITE

 

• Chemistry: Zn2(Fe, Mn)(PO4)2 - 4H2O , Hydrated Zinc Iron Manganese Phosphate.
• Class: Phosphates
• Uses: As collector's gemstone and as mineral specimens.
• Specimens

Phosphophyllite, whose cumbersome name means "phosphate leaf" in allusion to both its chemistry and cleavage, is a rare zinc and manganese mineral that is found at only a few localities. It can be most appreciated when cut into gemstones that possess a good blue-green color. Gemmy phosphophyllite comes from its Bolivian locality where it formed as a primary precipitate in tin rich hydrothermal veins. In Germany and in New Hampshire, it is found as an alteration product of primary phosphates such as triphylite.

 

PHYSICAL CHARACTERISTICS:

• Color is blue-green to colorless, gray or black (the latter probably from inclusions).
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System is monoclinic; 2/m.
• Crystal Habits include equant to prismatic individual crystals. Twinning is common and produces a fishtail contact twin.
• Cleavage is perfect in one direction and distinct in another.
• Fracture is conchoidal.
• Hardness is 3 - 3.5
• Specific Gravity is approximately 3.1 (slightly above average for translucent minerals)
• Streak is white.
• Associated Minerals include triphylite, cassiterite, mica and sulfide ores.
• Notable Occurrences are limited to San Luis Potosi, Bolivia; Palermo Mine, North Groton, New Hampshire, USA and Hagendorf, Germany.
• Best Field Indicators are crystal habit, cleavage, locality and color.

 

THE MINERAL PHOSPHURANYLITE

 

• Chemistry: Ca(UO2)3(PO4)2(OH)2 - 6H2O , Hydrated Calcium Uranyl Phosphate Hydroxide.
• Class: Phosphates
• Uses: As a very minor ore of uranium and as mineral specimens.
• Specimens

Phosphuranylite is one of many yellow, encrusting, non-fluorescent uranium bearing minerals and is unfortunately difficult to distinguish from the others. It has been found as an actual replacement for wood along with other uranium minerals. The uranium requires a reducing environment in order to precipitate out of solution and rotting, buried wood provides such an environment. Other occurrences of phosphuranylite are the result of alteration of primary uranium minerals such as uraninite, a uranium oxide. Often some black uraninite is left as an interior core surrounded by phosphuranylite and the fluorescent autunite. Remember this is a radioactive mineral and as such should be kept separated from other minerals that might be damaged by the radioactivity and of course human exposure should be limited!

 

PHYSICAL CHARACTERISTICS:

• Color is deep golden to straw yellow.
• Luster is vitreous.
• Transparency crystals are generally translucent.
• Crystal System is orthorhombic; 2/m 2/m 2/m.
• Crystal Habits include tiny platy crystals, crusts and fossil wood replacement masses.
• Cleavage is perfect in one direction (basal).
• Fracture is earthy
• Hardness is 2.5
• Specific Gravity is approximately 4.1 (well above average for translucent minerals)
• Streak is yellow.
• Other Characteristics:Radioactive and non-fluorescent.
• Associated Minerals include torbernite, autunite, uraninite and other uranium bearing minerals.
• Notable Occurrences include the Flat Rock Pegmatite and Buchanan Pegmatite, Spruce Pine, Mitchell County, North Carolina and the Jack Daniels No. 1 Mine, Coconino County, Arizona and the Ruggles Mine of Grafton and the Palermo Mine, North Groton, New Hampshire, USA; Spain; Republic of Congo; Bavaria, Germany; Margnac, Haute-Vienne, France and Rio Grande de Norte, Brazil.
• Best Field Indicators are crystal habit, non-fluorescence, associations, radioactivity and color.

 

THE MINERAL PICROMERITE

 

• Chemistry: K₂Mg(SO₄)₂ - 6H₂O, Hydrated Potassium Magnesium Sulfate.
• Class: Sulfates
• Group: Picromerite
• Uses: As a minor source of magnesium and as mineral specimens.
• Specimens

Picromerite, also known as "schoenite", forms in marine evaporite deposits where sea water has been concentrated and exposed to prolonged evaporation. Other marine evaporite minerals include calcite, dolomite, gypsum, anhydrite, halite, kieserite, polyhalite, kainite, carnallite and sylvite. Evaporite minerals are geologically important because they clearly are related to the environmental conditions that existed at the time of their deposition, namely arid. They also can be easily recrystallized in laboratories enabling sedimentologists to obtain their specific characteristics of formation. Picromerite is also found as a crusty deposit around fumaroles and in some dry caves. Specimens of picromerite in dry air will dehydrate forming the mineral langbeinite and will turn cloudy. For this reason specimens of picromerite should be stored in sealed containers.

Picrmerite lends its name to a group of sulfates called the Picrmerite Group. These sulfates are all monoclinic, have medium to large sized cations and have six water molecules. The general formula of this group is A₂B(SO₄)₂ - 6H₂O. The A cation can be either potassium or ammonium, NH₄. The B cation can be either iron, copper, magnesium and/or nickel.

These are the members of the Picromerite Group:

• Boussingaultite (Hydrated Ammonium Magnesium Sulfate)
• Cyanochroite (Hydrated Potassium Copper Sulfate)
• Mohrite (Hydrated Ammonium Iron Sulfate)
• Nickel-boussingaultite (Hydrated Ammonium Nickel Magnesium Sulfate)
• Picromerite (Hydrated Potassium Magnesium Sulfate)

 

THE PHYSICAL CHARACTERISTICS OF PICROMERITE:

• Color is white, colorless, reddish, gray or yellowish.
• Luster is vitreous.
• Transparency: Specimens are translucent to opaque.
• Crystal System is monoclinic; 2/m.
• Crystal Habits include granular, earthy and encrusting masses. Individual short prismatic crystals are rare.
• Cleavage is perfect.
• Fracture is conchoidal.
• Hardness is 2.5
• Specific Gravity is approximately 2.0 - 2.1 (light even for translucent minerals).
• Streak is white.
• Other Characteristics: Bitter taste.
• Associated Minerals include trona, blodite, halite, alunite, thernardite, sylvite and other more rare evaporite minerals.
• Notable Occurrences include Mt. Etna, Sicily and Mt. Vesuvius, Napoli, Campania, Italy as well as Galicia, Poland and Stassfurt, Saxony, Germany.
• Best Field Indicators are associations, density, habit, fracture and environment of formation.

   

THE MINERAL PIRSSONITE

 

• Chemistry: Na₂Ca(CO₃)₂ - 2H₂O , Hydrated Sodium Calcium Carbonate.
• Class: Carbonates
• Uses: Only as mineral specimens.
• Specimens

Pirssonite is named after American geologist Louis Valentine Pirsson. Pirssonite is one of several carbonate minerals that form in non-marine evaporite deposits. Other evaporite carbonates include trona, gaylussite, northupite, nahcolite and thermonatrite. Evaporite minerals are geologically important because they clearly are related to the environmental conditions that existed at the time of their deposition, namely arid. They also can be easily recrystallized in laboratories in order to confirm their specific characteristics of formation.

Pirssonite and gaylussite, Na₂Ca(CO ₃)₂ - 5H₂O, differ only in the number of water molecules, yet their symmetries are quite different. This is an indication of a change in their respective crystal structures. The two are best distinguished by their crystal habits in which pirssonite has a distinctive tabular diamond-shaped crystal form. Pirssonite can lose its water molecules and specimens should be stored in a sealed container.

 

PHYSICAL CHARACTERISTICS:

• Color is colorless, white or yellowish.
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent.
• Crystal System is orthorhombic.
• Crystal Habits include prismatic and tabular diamond-shaped or distorted hexagon-shaped crystals, but also massive and encrusting.
• Fracture is conchoidal.
• Hardness is 3 - 3.5
• Specific Gravity is 2.4 (slightly below average)
• Streak is white.
• Associated Minerals include gaylussite, northupite, trona, analcime and halite.
• Notable Occurrences include the type locality at Searles Lake, San Bernardino County, California as well as Deep Spring Lake, Inyo County and Borax Lake, Lake County, California, USA; Mont Saint-Hilaire, Quebec, Canada and elsewhere.
• Best Field Indicators: Crystal habit, environment of formation, density and locality.

 

 

 

 

 

THE MINERAL PLANCHEITE

 

• Chemistry: Cu8Si8O22(OH)4 - H2O, Hydrated Copper Silicate Hydroxide
• Class: Silicates
• Subclass: Inosilicates
• Uses: A very minor ore of copper and as mineral specimens.
• Specimens

Plancheite is another in the long list of secondary copper minerals.And like so many of them, this one is colorful, attractive, has interesting crystal habits and is definitely a good collection mineral.Its almost turquoise-like color is unique and its typical fibrous, radial habit makes for simply a one-of-a-kind mineral. It is named for J. Planche, who first brought specimens of plancheite from the Congo region to the mineralogical community.Plancheite can be found with other colorful secondary copper minerals such as dioptase, shattuckite, conichalcite, brochantite and chrysocolla,making some specimens a treasure trove of rare minerals.

 

PHYSICAL CHARACTERISTICS:

• Color is commonly a pale blue, greenish blue to almost turquoise blue and dark blue in some specimens.
• Luster is vitreous to silky.
• Transparency specimens are translucent to opaque.
• Crystal System is orthorhombic.
• Growth Habits include spherulites or sprays of acicular or fibrous radial crystal clusters. Other habits include massive, mammillary and fibrous aggregates and tiny tabular or platy crystals.
• Cleavage is not discernible
• Fracture is fibrous
• Hardness is 5.5.
• Specific Gravity is approximately 3.6 - 3.8 (above average for a non-metallic mineral).
• Streak is pale blue.
• Associated Minerals are cerussite, dioptase, limonite, melanotekite, quartz, shattuckite, bindheimite, conichalcite, brochantite, "bisbeeite"; (a variety of chrysocolla), and other chrysocolla varieties, and other secondary copper minerals.
• Notable Occurrences include the type locality of Mindouli, Congo as well as Tantara and Kambowe, Shaba, of the Democratic Republic of Congo and several copper deposits in Arizona, especially the Table Mountain Mine.
• Best Field Indicators are color, crystal habit, density, locality and associations.
•  

 

 

              

NATIVE PLATINUM

 

• Chemistry: Pt, Elemental Platinum
• Class: Elements
• Group: Platinum
• Uses: Important ore of platinum and other rare metals. Platinum metal is used for jewelry, chemical and other industrial uses as well as a currency stabilizer.
• Specimens

Native platinum is an exotic mineral specimen and an expensive metal. Unfortunately, well formed crystals of platinum are very rare and the common habit of platinum is nuggets and grains. Pure platinum is unknown of in nature as it usually is alloyed with other metals such as iron, copper, gold, nickel, iridium, palladium, rhodium, ruthenium and osmium. The presence of these other metals tends to lower the density of platinum from a pure metal specific gravity of 21.5 to as low as 14 and very rarely any higher than 19 in natural specimens. Few of these rarer metals form significant deposits on their own and thus platinum becomes the primary ore of many of these metals. The presence of iron can lead to a slight magnetism in platinum nuggets and is a common enough property to be considered diagnostic.

The element platinum is extremely scarce in most crustal rocks, barely seen as even a trace element in chemical analysis of these rocks. However platinum seems to be much more concentrated in the mantle and can be enriched through magmatic segregation. Platinum's origin in the crust is from ultra-mafic igneous rocks and therefore platinum is associated with minerals common to these rocks such as chromite and olivine. Platinum's most common source however is from placer deposits.

Over the ages, the platinum became weathered out of the igneous rocks and were tumbled down streams and rivers where the extremely heavy grains and nuggets of platinum collect behind rocks and bends in the rivers and streams. These deposits, called placers, that form behind the rocks and bends are enriched in heavy grains as lighter material is carried further down stream. The heaviest grains are the nuggets of gold, platinum and/or other heavy minerals.

The metal platinum is a valuable metal that is gaining in importance. It is typically more expensive by weight than gold, mostly a product of its scarcity. Platinum is very non-reactive and for this reason it is used in chemical reactions as a catalyst. Metallic platinum can facilitate many chemical reactions without becoming altered in the process. It is also used in many anti-pollution devices, most notable is the catalytic converter, and has been given the nick name the "Environmental Metal". Native platinum is the primary ore of platinum, but deposits containing the rare platinum arsenide, sperrylite of the Pyrite Group, have made a huge contribution to the world's limited supply.

 

 

PHYSICAL CHARACTERISTICS:

• Color is a white-gray to silver-gray, usually lighter than the platinum color of pure processed platinum.
• Luster is metallic.
• Transparency is opaque.
• Crystal System: Isometric; 4/m bar 3 2/m
• Crystal Habits include nuggets, grains or flakes, rarely showing cubic forms.
• Cleavage is absent.
• Fracture is jagged.
• Hardness is 4 - 4.5
• Specific Gravity is 14 - 19+, pure platinum is 21.5 (extremely heavy even for metallic minerals).
• Streak is steel-gray.
• Other Characteristics: Does not tarnish, is sometimes weakly magnetic and is ductile, malleable and sectile, meaning it can be pounded into other shapes, stretched into a wire and cut into slices.
• Associated Minerals include chromite, olivine, enstatite, pyroxene, magnetite and occasionally gold.
• Notable Occurrences includes Transvaal, South Africa; Ural Mountains, Russia; Columbia and Alaska, USA.
• Best Field Indicators are color, density, weak magnetism, hardness, associations and ductility.

 

 

THE MINERAL PLATTNERITE

 

• Chemistry: PbO2, Lead Oxide
• Class: Oxides and Hydroxides
• Group: Rutile
• Uses: A very minor ore of lead and as mineral specimens.
• Specimens

Plattnerite is a relatively scarce mineral. It is a lead oxide of very simple formula, PbO2. The lead content makes an appreciable impact on plattnerite's properties. First off, plattnerite has an extremely high specific gravity of 9.4 for obvious reasons. Secondly, the luster of plattnerite is very high due to the lead content. This is not a surprise when you consider that lead is added to fine glass crystal in order to increase its luster or sparkle. The luster of plattnerite is adamantine to submetallic.

Typical plattnerite is massive, but occasionally relatively large prismatic crystals are seen. Most rock shop specimens are drusy crusts of tiny black plattnerite crystals that have a nice sparkling sheen.

 

PHYSICAL CHARACTERISTICS:

• Color is black.
• Luster is adamantine to submetallic.
• Transparency: Crystals are opaque.
• Crystal System is tetragonal; 4/m 2/m 2/m
• Crystal Habits include eight sided prisms and blocky crystals terminated by a blunt four sided or complex pyramid. Large crystals are rare and massive forms are more common. It also forms as drusy crusts with tiny sparkling crystals.
• Cleavage is good in two directions forming prisms, poor in a third (basal).
• Fracture is conchoidal to uneven.
• Hardness is 5 - 5.5
• Specific Gravity is 9.4+ (very heavy even for a metallic mineral)
• Streak is "chestnut" brown
• Other Characteristics: Can be dissolved by acids.
• Associated Minerals are rosasite, limonite, murdochite and other lead oxides.
• Notable Occurrences include Leadhills, Lanarkshire, Scotland; Shoeshone Co., Idaho, USA and Mapimi, Mexico.
• Best Field Indicators are crystal habit, streak, density, color and high luster.

 

     

THE MINERAL POLYBASITE

 

• Chemistry: (Ag, Cu)16Sb2S11, Silver Copper Antimony Sulfide
• Class: Sulfides
• Subclass: Sulfosalts
• Uses: An ore of silver and as mineral specimens.
• Specimens

Polybasite is a somewhat uncommon silver bearing mineral. Although not a well known ore of silver, it is never-the-less a locally important ore in some mines. It forms interesting crystals that have a pseudohexagonal outline with rhombohedral striations. Although its symmetry is monoclinic, the nearly hexagonal crystals and striations suggest that it has a higher temperature phase that is hexagonal or trigonal.

Polybasite is in what is called a solid solution series with the mineral pearceite, (Ag, Cu)16As2S11. The two minerals can substitute the antimony for the arsenic within their structures. However, pearceite is far more rare than polybasite possibly indication that antimony is more stable in this structure. The solid solution series is similar to the one for pyrargyrite-proustite. Two other silver sulfosalts.

Polybasite is difficult to distinguish from the minerals hematite, an oxide, and another silver antimony sulfide, stephanite. Hematite forms metallic steel gray platy crystals but has a blood-red streak and is considerably harder. Stephanite lacks the rhombic striations (on the pinacoidal faces), the red flashes and the good cleavage of polybasite.

 

PHYSICAL CHARACTERISTICS:

• Color is an iron black to a "cherry" red in thin slices with slight flashes of red possibly seen on some crystal surfaces.
• Luster is metallic.
• Transparency: Crystals are opaque to translucent in thin slices or at crystal edges.
• Crystal System: Monoclinic; 2/m
• Crystal Habits include pseudohexagonal plates or tablets, also massive.
• Cleavage is perfect in one direction (basal).
• Fracture is uneven.
• Hardness is 2 - 3
• Specific Gravity is approximately 6.1 - 6.3 (heavy even for metallic minerals)
• Streak is a black to reddish-black.
• Other Characteristics: Partially malleable, crystals will show a rhombic striation pattern at times and a dark coating can often form after prolonged exposure to light (can be removed by ultrasonic treatment).
• Associated Minerals include silver, quartz, galena, proustite, pyrargyrite, stephanite, tetrahedrite , acanthite and other silver sulfide minerals.
• Notable Occurrences include Las Chiapas, Guanajuato and Arizpe, Sonora, Mexico; Saxony, Germany; Colorado and Nevada, USA; Atacama, Chile; Bolivia; Australia and Sardinia.
• Best Field Indicators are crystal habit, density, softness, cleavage, association with other silver sulfosalts and color.

 

 

 

THE MINERAL POLYHALITE

 

• Chemistry: K₂Ca₂Mg(SO₄)₄ - 2H₂O, Hydrated Potassium Calcium Magnesium Sulfate.
• Class: Sulfates
• Uses: As a minor source of potassium and as mineral specimens.
• Specimens

Polyhalite is named in allusion to its many metal ions in its formula or literally translated "many salts". Polyhalite is a potassium, calcium and magnesium sulfate salt. Although it is an evaporite mineral, polyhalite is otherwise not related to the mineral halite. It forms in marine evaporite deposits where sea water has been concentrated and exposed to prolonged evaporation. Polyhalite precipitates only after calcite, dolomite, gypsum, anhydrite and halite have precipitated first. This does not occur often as it requires significant evaporation, but some extensive beds of potassium evaporates have formed and are excavated for their potassium content. Other potassium evaporates include kainite, picromerite, carnallite and sylvite.

Polyhalite is relatively easy to distinguish from other evaporates. Its taste is bitter, unlike halite. It does not completely dissolve in water leaving a calcium sulfate residue, unlike sylvite. It gives a purple flame result when it is put is a gas flame due to its potassium content, unlike kieserite and other non-potassium salts. Evaporite minerals are geologically important because they clearly are related to the environmental conditions that existed at the time of their deposition, namely arid. They also can be easily recrystallized in laboratories in order to postulate their specific characteristics of formation.

 

PHYSICAL CHARACTERISTICS:

• Color is white, colorless or gray. Iron oxides may color specimens red, brick-red or pink.
• Luster is vitreous to resinous.
• Transparency: Crystals are transparent to translucent.
• Crystal System is triclinic: bar 1.
• Crystal Habits include fibrous, lamellar, granular and foliated masses. Individual crystals are rare.
• Cleavage is perfect in one direction.
• Fracture is fibrous or splintery.
• Hardness is 3.5
• Specific Gravity is approximately 2.8 (average for translucent minerals).
• Streak is white.
• Other Characteristics: Does not completely dissolved in water leaving a residue, has a bitter taste and can color a flame purple (for potassium).
• Associated Minerals include halite, anhydrite, kainite, carnallite, sylvite and other more rare potassium evaporite minerals.

 

THE MINERAL POLYLITHIONITE

 

• Chemistry: KLi2AlSi4O10F2, Potassium Lithium Aluminum Silicate Fluoride.
• Class: Silicates
• Subclass: Phyllosilicates
• Group: Micas
• Division: True Micas
• Uses: Only as mineral specimens.
• Specimens

Polylithionite, which is named from the Greek for having much lithium, is not a well know mineral. Yet it is an attractive mineral that is available on the mineral markets. The best specimens arguably come from the famous quarry at Mont Saint-Hilaire, Quebec, Canada. Specimens there are found mostly in the altered and unaltered pegmatites with other rare minerals. Polylithionite is found at other alkaline rich pegmatitic deposits such as the Ilimaussaq alkaline complex in Greenland and at Langesundsfjord, Norway. Polylithionite is fluorecent lemon yellow and this makes distinguishing it from most other micas rather easy. Its habit to form rosettes is distinctive as well. Any yellow to silvery white, fluorescent mica like crystals attached to specimens of other Mont Saint-Hilaire specimens are probably polylithionite.

Polylithionite is certainly not one of the more well know mica minerals. It is a true mica closely related to other lithium rich micas; lepidolite and tainiolite.Polylithionite, like other micas, has a layered structure of lithium aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Polylithionite's rarity, associations with other rare minerals, attractive color and fluorescent color and crystal habit make it an ideal collection mineral.

 

PHYSICAL CHARACTERISTICS:

• Color is colorless, white, bluish, greenish, yellow, brown, pink, silvery to pearly white.
• Luster is pearly to waxy.
• Transparency crystals are transparent to translucent.
• Crystal System is monoclinic; 2/m
• Crystal Habits include pseudohexagonal tabular to platy crystals forming "books" and rosettes.
• Cleavage is perfect in one direction producing thin sheets or flakes.
• Fracture is not readily observed due to cleavage but is uneven.
• Hardness is 2 - 3.
• Specific Gravity is approximately 2.6 - 2.8 (average)
• Streak is white.
• Other Characteristics: Specimens are fluorecent lemon yellow under shortwave UV light.
• Associated Minerals are many and include catapleiite, ilmenite, behoite, titanite, aragonite, eudialyte, leucosphenite, fluorite, willemite, apophyllite, rhodochrosite, steacyite, leifite, sodalite, pyrochlore, calcite, sugilite, microcline, axinite, manganbabingtonite, galena, ancylite, natrolite, serandite, hilairite, sheldrickite and calcioancylite.
• Notable Occurrences include the type locality of Kangerdluarsuk, Ilimaussaq alkaline complex, Greenland as well as Langesundsfjord, Norway; Varutrask, Sweden; Washington Pass, Okanogan County, Washington; Landsman Camp, Graham County, Arizona and Point of Rocks, New Mexico, USA; Dara-i-Poiz Massif, Tadzhikistan and of course Mont Saint-Hilaire, Quebec, Canada.
• Best Field Indicators are crystal habit, fluorescence, color, cleavage, locality and associations.

 

 

 

  

THE MINERAL POWELLITE

 

• Chemistry: CaMoO₄, Calcium Molybdenate
• Class: Sulfates
• Subclass: Molybdenates
• Uses: As a minor ore of molybdenum (an important industrial metal) and as mineral specimens.
• Specimens

Powellite is one of only a handful of relatively common molybdenum minerals. Other molybdenum minerals include wulfenite, molybdenite, ferrimolybdite, molybdite and sidwellite. Powellite is named for the American geologist, Major John Wesley Powell, a former director of the U. S. Geological Survey. Most of powellite's occurrences are the result of hydrothermal reactions with the primary sulfide mineral molybdenite, with a formula of MoS₂. Powellite in fact, forms pseudomorphs after molybdenite. A pseudomorph is an atom by atom replacement of one mineral's chemistry for another; all the while the crystal retains the outward shape of the original mineral (pseudomorph means "false shape"). These pseudomorphs will have the shape of molybdenite crystals, but are actually made of powellite. Powellite also is known to form as a primary mineral in quartz veins.

Powellite forms an incomplete series with the mineral scheelite, CaWO₄. Scheelite differs from powellite by the substitution of the molybdenum in powellite by the tungsten (W) in scheelite. Some tungsten is usually found in powellite and thus sometimes the formula of powellite is written as Ca(Mo, W)O₄ to reflect this substitution. Scheelite is a popular fluorescent mineral as it typically glows a bright bluish white. Powellite is less well known for its fluorescence, but some specimens can display a delightful golden yellow under ultraviolet light. Crystals of powellite resemble the much more common but heavier crystals of scheelite, fortunately the difference in fluorescence is a key to distinguishing them. Powellite, scheelite and the silicate mineral scapolite all belong to an exclusive symmetry class called the Tetragonal Dipyramidal Class with a symmetry of 4/m.

 

PHYSICAL CHARACTERISTICS:

• Color is yellow, brown, gray, blue, white or black.
• Luster is adamantine to greasy.
• Transparency: Crystals are translucent to transparent.
• Crystal System is tetragonal; 4/m
• Crystal Habits include small four sided pyramidal crystals (pseudo-octahedral) and thin plates. Commonly as crusts or films around altered molybdenite and as pseudomorphs after molybdenite.
• Cleavage is distinct in four directions (bipyramidal).
• Fracture is uneven.
• Hardness is 3.5 - 4.
• Specific Gravity is approximately 4.2 - 4.3 (heavy for nonmetallic minerals).
• Streak is white.
• Other Characteristics: Fluorescent golden yellow.
• Associated Minerals are quartz, zeolites, molybdenite and lindgrenite.
• Notable Occurrences include the Peacock Lode, Seven Devils district, Idaho (the type locality); Keewenaw Peninsula, Michigan; Tungsten, Nevada; Superior, Arizona and Randsberg, California, USA; Nasik, India; Turkey; Russia; Scotland; Clayton Quarry, Panama Canal Zone, Panama and Morocco.
• Best Field Indicators are crystal habit, color, fluorescence, association with molybdenite and cleavage.

THE MINERAL
PREHNITE

• Chemistry: Ca₂ Al₂ Si₃ O₁₀(OH)₂, Calcium Aluminum Silicate Hydroxide.
• Class: Silicates
• Subclass: Phyllosilicates
• Uses: As mineral specimens and limited use for ornamental stone purposes.
• Specimens

Prehnite was named after its discoverer; Colonel Hendrik von Prehn and is an attractive collection mineral that is occassionally used for ornamental stone purposes. Its color is usually a pleasant green and is at times quite unique to prehnite. Typical prehnite forms rather thick crusts with a rough or crystaline texture. Epimorphs (crystal growth over the surface of another mineral) over laumontite crystals are interesting and attractive. Usually the laumontite has dissolved away leaving the hollow crust of prehnite behind.

-

PREHNITE EPIMORPHS AFTER LAUMONTITE

Prehnite is often found with zeolites and is sometimes thought of as a zeolite. But zeolites are actually tectosilicates and prehnite is a member the Phyllosilicates Subclass. However, like zeolites, prehnite can give off water when heated, but can not gain the water back like they can. Like most zeolites, prehnite is formed as a result of low grade metamorphism usually from hydrothermal solutions. Crystals can be found in cavities of mafic igneous rocks.

Minerals that can be confused with prehnite include gyrolite, smithsonite and hemimorphite. Prehnite is harder than all of these and lacks smithsonite's unusual luster. Hemimorphite is usually blue and gyrolite is not as glassy. Prehnite can be associated with many beautiful minerals and can make a fine specimen on its own. Its color, luster, associations and crystal habits make it a joy to own.

 

PHYSICAL CHARACTERISTICS:

• Color is usually a pale green to a yellowish grass green, also gray, white or colorless.
• Luster is vitreous to waxy or pearly.
• Transparency: Crystals are transparent to mostly translucent.
• Crystal System is orthorhombic; 2 m m.
• Crystal Habits include nodular, concretionary, radial, encrusting and stalactitic formations among other similar types. Tabular or pyramidal individual crystals are rare but some nodular specimens show tabular crystal protrusions. Epimorphs (crystal growth over the surface of another mineral) over laumontite are usual, but available (see above).
• Cleavage is good in one direction (pinacoidal).
• Fracture is uneven.
• Hardness is 6 - 6.5.
• Specific Gravity is approximately 2.9+ (average).
• Streak is white.
• Other Characteristics: Lacks the luster of smithsonite and cleavage surfaces are curved and pearly.
• Associated Minerals include datolite, gyrolite, fluorapophyllite, quartz, calcite, copper, pectolite, stilbite and other zeolites.
• Notable Occurrences include the type locality of Cape of Good Hope, South Africa as well as Connecticut; Pennsylvania; Patterson, New Jersey and Centreville, Virginia, USA; Bombay, India; Harz Mountains, Germany; Austria; Scotland; Copper Valley, Namibia; Jeffery Quarry, Asbestos, Canada; China; New South Wales, Australia and France.
• Best Field Indicators are crystal habit, color, cleavage, hardness and associations.

 

  

THE MINERAL PROUSTITE

 

• Chemistry: Ag3AsS3, Silver Arsenic Sulfide
• Class: Sulfides
• Subclass: Sulfosalts
• Uses: A minor ore of silver, as mineral specimens and as a rare gemstone.
• Specimens

Proustite is one of only an few sulfides that are not metallic or opaque. In fact it is at times cut for gemstones, although it is far too soft to wear in everyday jewelry. Its color is a bright scarlet red to reddish orange and is distinctive. The nickname "Ruby Silver" has been applied to proustite as well as the closely related mineral pyrargyrite.

Pyrargyrite is a silver antimony sulfide and is isostructural with proustite. Isostructural means that the two minerals have the same structure but a different chemistry. There is some substitution of the antimony and arsenic. But in both minerals, the substitution is minor and no solid solution is believed to exist between the two minerals.

Proustite is the rarer of the two minerals and is usually found in the same ore veins with pyrargyrite, silver and other silver sulfides. Fine crystals, with their transparency, luster and color, are very attractive mineral specimens. However, as with other silver minerals, it is reactive to light and can form a white coating upon exposure. This coating can be wiped off, but fine specimens should be stored in closed containers with exposure to light limited.

 

PHYSICAL CHARACTERISTICS:

• Color is a bright scarlet red to reddish orange.
• Luster is adamantine.
• Transparency: Crystals are translucent to transparent.
• Crystal System is trigonal; 3 m
• Crystal Habits: include prismatic crystals with rhombohedral and scalenohedral faces forming terminations. There is no perpendicular mirror plane and therefore a hemimorphic crystal can be seen, in some rare examples, with differing terminations at the top and bottom of the crystal. Also found massive.
• Cleavage is sometimes distinct in three directions forming rhombohedrons.
• Fracture is conchoidal.
• Hardness is 2 - 2.5
• Specific Gravity is approximately 5.6 (very heavy for translucent minerals)
• Streak is red.
• Associated Minerals include pyrargyrite, silver, tetrahedrite, calcite, quartz, galena, sphalerite and other silver vein minerals.
• Other Characteristics: A white film forms on the surface of crystals upon exposure to light.
• Notable Occurrences include Atacama, Chile; silver mines in Saxony Germany; Poorman Mine, Idaho and Chihuahua, Mexico.
• Best Field Indicators are crystal habit, density, association with pyrargyrite and color.

 

 

 

THE MINERAL PSEUDOBOLEITE

 

• Chemistry: Pb₅Cu₄Cl₁₀(OH)₈ - 2H₂O,

Hydrated Lead Copper Chloride Hydroxide

• Class: Halides
• Uses: A very minor ore of copper and lead and as mineral specimens.
• Specimens

Pseudoboleite is a mineral that is often intergrown with its "false" self. It is closely related to boleite, whose cumbersome formula is Pb₂₆Cu₂₄Ag₁₀Cl₆₂(OH) ₄₈ - 3H₂O. Pseudoboleite gets its name by being a false boleite (pseudo means false). Boleite was named for Boleo, Santa Rosalia, Baja California, Mexico which is the type locality for both minerals. The French colonial town of Santa Rosalia was built near the copper mines that extracted copper from the unusual sedimentary copper deposits. Pseudoboleite and boleite specimens can still be found in these deposits although they are scarce and not easy to find. Pseudoboleite forms tiny blocky crystals on top of the boleite's crystal faces that are called epitaxial overgrowths. Pseudoboleite is often intergrown with boleite inside these crystals in an example of parallel growth. The two minerals are also known to be intergrown with the mineral cumengite, (Pb₂₁Cu₂₀Cl₄₂ (OH)₄₀).

All three minerals are very rare and have very unusual chemistries. These halides and others with similar chemistries belong to a division in the Halides Class called the Oxyhalides and Hydroxyhalides. These minerals have either oxygen or hydroxide groups in their chemistries. The oxygen atom in their chemistries might require their classification in the Oxides Class of minerals except that their structures are more tied to the halide elements and the oxygens and hydroxides are kind of superfluous to the overall structure. Some other members of the Oxyhalides and Hydroxyhalides include bideauxite, chloroxiphite, kelyanite, botallackite, laurionite, paralaurionite, mendipite, fiedlerite, pinchite, penfieldite, yedlinite, atacamite, koenenite, diaboleite, zirklerite and paratacamite. Of these, only atacamite and boleite are common enough to be seen at rock shows and in rock shops with regularity.

 

PHYSICAL CHARACTERISTICS:

• Color is indigo blue.
• Luster is vitreous to pearly.
• Transparency: Crystals are usually translucent to transparent.
• Crystal System is tetragonal; 4 2 2
• Crystal Habits include tiny blocky crystals on top of the boleite's crystal faces; a form of epitaxial overgrowth. It is often intergrown with boleite in parallel growth. Crystals can be pseudocubic.
• Cleavage is perfect.
• Fracture is uneven.
• Hardness is 2.5
• Specific Gravity is 4.9 - 5.0 (rather heavy for translucent minerals)
• Streak is light green to blue.
• Associated Minerals include other rare copper and lead chlorides such as boleite, cumengite, chloroxiphite, paralaurionite, matlockite, chlorargyrite, atacamite, mendipite and diaboleite. Also found with cerussite, smithsonite, connellite, gerhardtite, cuprite, leadhillite, clays, linarite, phosgenite and chrysocolla.
• Notable Occurrences include Boleo, Santa Rosalia, Baja California, Mexico and the Mammoth District, Arizona, USA and most places where boleite is found.
• Best Field Indicators are crystals habit, color, density, streak and locality.

 

THE MINERAL PSEUDOBROOKITE

 

• Chemical Formula: Fe2TiO5, Iron Titanium Oxide
• Class: Oxides and Hydroxides
• Uses: A very minor ore of titanium and as mineral specimens.
• Specimens

Pseudobrookite is a rare and interesting mineral for collectors. It forms needle thin, acicular, crystals that form in sprays of several individuals. Its high luster, due to the titanium content, is rather nice and its rarity makes pseudobrookite an appreciated mineral in most anyone's collection. Pseudobrookite is associated with many interesting minerals such as pyroxenes, hornblende, tridymite, topaz, hematite and bixbyite. Most of the more popular of these assortments are found in cavities in rhyolitic rock and make for attractive and much sought after mineral specimens. Nice pseudobrookite specimens come from the Thomas Range in Utah.

 

PHYSICAL CHARACTERISTICS:

• Color is dark black.
• Luster is metallic to adamantine.
• Transparency: Crystals are opaque.
• Crystal System is monoclinic; 2/m
• Crystal Habits include small acicular or thin prismatic crystals aggregated together in sprays of only a few individuals or singular. Also tabular.
• Cleavage is indistinct in one direction.
• Fracture is conchoidal.
• Hardness is 6
• Specific Gravity is 4.4 (average for metallic minerals)
• Streak is brownish to reddish yellow.
• Associated Minerals include spessartine, pyroxenes, hornblende, tridymite, hematite, bixbyite and topaz.
• Notable Occurrences are limited to the Thomas Range, Utah and Piski, Transylvania, Romania.
• Best Field Indicators are crystal habit, streak, associations and locality.

 

 

THE MINERAL PSEUDOMALACHITE

 

• Chemistry: Cu5(PO4)2(OH)4, Copper Phosphate Hydroxide.
• Class: Phosphates
• Uses: as a very minor ore of copper and as mineral specimens.
• Specimens

Pseudomalachite, as its name implies, is not malachite, but a false malachite. It is not related to malachite at all being a phosphate mineral and malachite being a carbonate. But there is a slight similarity in their respective formula.

• PSEUDOMALACHITE - Cu5(PO4)2(OH)4
• MALACHITE - Cu4(CO3)2(OH)4

Malachite's formula is usually written as Cu2CO3(OH)2 but if doubled, it will appear closer to that of pseudomalachite. Pseudomalachite has an extra copper to balance the extra -2 charge of the two phosphate ion groups. Both minerals have the same crystal symmetry, but different structures.

Pseudomalachite was named "false malachite" because it is visually similar in appearance to malachite. The dark green waxy botryoidal specimens of pseudomalachite are indeed reminiscent of botryoidal malachite. Both minerals are formed in the oxidation zone of copper ore deposits and are in fact associated with each other. But the much rarer pseudomalachite lacks the characteristic light and dark green banding of malachite and is slightly harder and more dense. To verify an identification, pseudomalachite will not react to warm hydrochloric acid as will malachite.

Pseudomalachite is trimorphous with the minerals ludjibaite and reichenbachite. A trimorph is a set of three minerals that all have the same chemistry, but they have different structures.

 

PHYSICAL CHARACTERISTICS:

• Color is a consistent dark green to blackish-green.
• Luster is vitreous to waxy.
• Transparency: Specimens are translucent to transparent.
• Crystal System is monoclinic; 2/m
• Crystal Habits include botryoidal masses and small prismatic or tabular crystals. Also found in radiating clusters, fibrous and in crusts.
• Cleavage is absent.
• Fracture is conchoidal.
• Hardness is 4.5 - 5.
• Specific Gravity is approximately 4.3 - 4.4 (above average).
• Streak is green.
• Other Characteristics: Does not effervesce with warm hydrochloric acid as does malachite.
• Associated Minerals include quartz, malachite, chrysocolla, brochantite, antlerite, jarosite, lepidocrocite, cornetite, atacamite and libethenite.
• Notable Occurrences include Shaba, Zaire; Libethen, Slovakia; Bavaria, Germany; France; Nizhniy Tagil'sk, Russia; Canada and several localities in Arizona, USA.
• Best Field Indicators are crystal habit, color, hardness, density, localities and lack of reaction to acid.

 

  

THE MINERAL PSILOMELANE

 

• Chemical Formula: No fixed formula, but sometimes Ba(Mn+2)(Mn+4)8O16(OH)4 is used, Barium Manganese Oxide Hydroxide
• Class: Oxides and Hydroxides
• Uses: an ore of manganese and as a mineral specimen
• Specimens

Psilomelane is a mineral name that is losing its significance. Still in use around the world the name is applied to hydrated barium bearing manganese specimens. It is probably a mixture of several minerals but is composed mostly of the mineral Romanechite, Ba(Mn+2, Mn+4)5O10-H2O. The difficulty in distinguishing romanechite from other barium manganese oxides, that are probably mixed together in the same specimen, is why the name psilomelane is still in use.

Psilomelane, although not as common as pyrolusite, is still an important ore of manganese. Manganese is a strategically valuable metal since it is an essential ingredient in steel and other alloys. The mining term "wad" is used to indicate ores that are a mixture of several manganese oxides such as psilomelane, pyrolusite and others that are difficult to distinguish.

Psilomelane is often banded with gray pyrolusite and the alternating layers make an attractive polished stone with bands of metallic gray and submetallic black. Psilomelane also forms tufts of hair-like aggregates that are similar to those produced by pyrolusite. However, the difference in luster between the two minerals is usually sufficient to distinguish them. Earthy specimens as well are difficult to differentiate since both minerals tend to have a dull luster when found in this habit. Fortunately pyrolusite's softness will give it away when it leaves marks on paper and fingers.

 

PHYSICAL CHARACTERISTICS:

• Color is variable from iron-black to bluish black to steel gray.
• Luster is submetallic to dull in earthy specimens.
• Transparency crystals are opaque.
• Crystal System is monoclinic.
• Crystal Habits include massive, fibrous, botryoidal, columnar, stalactitic, concretionary, powdery and earthy.
• Cleavage is absent.
• Fracture is conchoidal to uneven.
• Hardness is 5 - 5.5.
• Specific Gravity is 4.4 - 4.5 (heavy for non-metallic minerals)
• Streak is black or brownish black.
• Other Properties: sometimes banded with the mineral pyrolusite producing alternating bands of metallic gray and submetallic black.
• Associated Minerals are barite, hematite, quartz, pyrolusite and other manganese oxide minerals.
• Notable Occurances include Austinville, Wythe County., Virginia, Upper Pennisula of Michigan and Tuscon, Arizona, USA; Schneeburg, Germany; Cornwall, England; Ouro Preto, Minas Gerias, Brazil and elsewhere.
• Best Field Indicators are habits, luster, hardness, color and streak.

   

THE MINERAL PUCHERITE

 

• Chemistry: BiVO4, Bismuth Vanadate.
• Class: Phosphate Class
• Subclass: Vanadates
• Uses: Only as mineral specimens
• Specimens

Pucherite, whose name comes from the actual mine shaft (Pucher Shaft) from where the first specimens were found, is a rare bismuth vanadate mineral. Pucherite is found at the Wolfgang Mine near Schneeburg in Saxony, Germany and a few other places. The Wolfgang Mine is the mine that contains the Pucher Shaft. The bismuth in this mineral has an effect similar to the presence of lead in other minerals. It increases both the density and luster. Pucherite has a significant specific gravity of around 6.5 and a bright adamantine luster.

Pucherite is trimorphous with two other minerals: dreyerite and clinobisvanite. All three minerals have the same chemistry, BiVO4, but they all have different structures. This is reflected in the fact that pucherite is orthorhombic, clinobisvanite is monoclinic and dreyerite is tetragonal in symmetry. The differing structures has a slight effect on the overall yellow color of the group. Since the chemistry is the same, any change in the color of pure samples must be due to the structural differences. Dreyerite is typically orange-yellow to brownish yellow while clinobisvanite is just yellow to yellowish red, but pucherite is a dark reddish brown to less likely brownish yellow.

 

PHYSICAL CHARACTERISTICS:

• Color is dark reddish brown to brownish yellow.
• Luster is vitreous to adamantine.
• Transparency: Crystals are transparent to translucent.
• Crystal System is orthorhombic.
• Crystal Habits include tabular well formed crystals with curved faces and sharp angles. Also acicular crystals and earthy masses.
• Cleavage is perfect.
• Fracture is conchoidal.
• Hardness is 4.
• Specific Gravity is approximately 6.3 - 6.7 (heavy for translucent minerals)
• Streak is yellow.
• Associated Minerals are limonite, bismite and bismuth.
• Notable Occurrences are limited to Schneeburg, Saxony, Germany and Brejauba, Minas Gerais, Brazil.
• Best Field Indicators are color, crystal habit, density, luster and associations.

 

   

THE MINERAL PURPURITE

 

• Chemistry: MnPO4, Manganese Phosphate
• Class: Phosphates
• Uses: Only as a mineral specimens.
• Specimens

Purpurite forms a series with the mineral heterosite. Purpurite is the manganese rich end member and heterosite is the iron rich end member. Purpurite is a very rare mineral that would get much attention in the semi-precious stone market due to its striking color, if it were not for this rarity. Purpurite is an alteration product of an equally rare mineral called lithiophyllite, LiMnPO4. The alteration takes place atom by atom and actually forms what is called a pseudomorph or "false shape". A pseudomorph is a mineral that has the shape of one mineral but has a different chemistry and/or structure.

The alteration is an oxidation reaction with the manganese ion going from a positive two (+2) charge in lithiophyllite to an ion with a positive three (+3) charge in purpurite. With the change in charge in the manganese ion, the lithium ion is then lost. Often some of the original lithiophyllite is still present in most purpurite specimens. The purple color or purpurite is truly unique in the mineral rainbow.

 

PHYSICAL CHARACTERISTICS:

• Color is purple (hence the name).
• Luster is vitreous to sub-metallic.
• Transparency: Crystals are translucent to opaque.
• Crystal System is orthorhombic; 2/m2/m2/m
• Crystal Habits generally are massive grains or crusts.
• Cleavage is good in one and poor in another direction.
• Fracture is uneven.
• Hardness is 4 - 4.5.
• Specific Gravity is approximately 3.3 (above average)
• Streak is deep red to purple.
• Other Characteristics: Brown coatings can be removed by weak acid baths that can also bring out more purple color.
• Associated Minerals are lithiophyllite, heterosite, quartz and feldspars.
• Notable Occurrences include Namibia; western Australia; North Carolina, USA and France.
• Best Field Indicators are color, associations, lack of crystals and luster.

 

 

THE MINERAL PYRARGYRITE

 

• Chemistry: Ag3SbS3, Silver Antimony Sulfide
• Class: Sulfides
• Subclass: Sulfosalts
• Uses: an ore of silver and as mineral specimens.
• Specimens

Pyrargyrite is a popular silver bearing mineral for collectors. Its color is a dark red and is most commonly so dark that it appears black. The nickname "Ruby Silver" has been applied to pyrargyrite although it is typically applied to the related mineral proustite.

Pyrargyrite is isostructural with proustite, a silver arsenic sulfide. Isostructural means that the two minerals have the same structure but a different chemistry. There is some substitution of the antimony and arsenic. But in both minerals, the substitution is minor and no solid solution is believed to exist between the two minerals.

Pyrargyrite is the more common of the two minerals and is usually found in the same ore veins with proustite, silver and other silver sulfides. Its crystals can be striking and very attractive. However, as with other silver minerals, it is reactive to light and can darken upon exposure, and a translucent specimen can quickly become essentially opaque. Therefore, fine specimens should be stored in closed containers with exposure to light limited.

 

 

PHYSICAL CHARACTERISTICS:

• Color is a dark red to red-black.
• Luster is adamantine.
• Transparency crystals are translucent to nearly opaque.
• Crystal System trigonal; 3m
• Crystal Habits: include prismatic crystals with rhombohedral and scalenohedral faces forming terminations. There is no perpendicular mirror plane and therefore a hemimorphic crystal can be seen, in some rare examples, with differing terminations at the top and bottom of the crystal. Typical crystals are poorly formed and modified heavily by secondary faces. Also found massive.
• Cleavage is sometimes distinct in three directions forming rhombohedrons.
• Fracture is conchoidal.
• Hardness is 2.5
• Specific Gravity is approximately 5.8 (very heavy for translucent minerals)
• Streak is a dark cherry red.
• Associated Minerals include proustite, silver, tetrahedrite, calcite, argentite. quartz, galena, sphalerite and other silver vein minerals.
• Other Characteristics: darkens upon exposure to light and crystals are frequently striated.
• Notable Occurances include Atacama, Chile; silver mines in Saxony Germany and in Colorado, USA and Cobalt, Onatario, Canada.
• Best Field Indicators are crystal habit, density, association with silver sulfides and color.

 

 

THE MINERAL PYRITE

 

• Chemistry: FeS2, Iron Sulfide
• Class: Sulfides
• Group: Pyrite
• Uses: A very minor ore of sulfur for sulfuric acid, used in jewelry under the trade name "marcasite" and as mineral specimens.
• Specimens

Pyrite is the classic "Fool's Gold". There are other shiny brassy yellow minerals, but pyrite is by far the most common and the most often mistaken for gold. Whether it is the golden look or something else, pyrite is a favorite among rock collectors. It can have a beautiful luster and interesting crystals. It is so common in the earth's crust that it is found in almost every possible environment, hence it has a vast number of forms and varieties.

Bravoite is the name given to a nickel-rich iron sulfide. It is closely related to pyrite but contains up to 20% nickel. Some mineral books treat it as a variety of pyrite.

Pyrite is a polymorph of marcasite, which means that it has the same chemistry, FeS2, as marcasite; but a different structure and therefore different symmetry and crystal shapes. Pyrite is difficult to distinguish from marcasite when a lack of clear indicators exists.

Pyrite's structure is analogous to galena's structure with a formula of PbS. Galena though has a higher symmetry. The difference between the two structures is that the single sulfur of galena is replaced by a pair of sulfurs in pyrite. The sulfur pair are covalently bonded together in essentially an elemental bond. This pair disrupts the four fold symmetry that a single atom of sulfur would have preserved and thus gives pyrite a lower symmetry than galena.

Although pyrite is common and contains a high percentage of iron, it has never been used as a significant source of iron. Iron oxides such as hematite and magnetite, are the primary iron ores. Pyrite is not as ecomonical as these ores possibly due to their tendency to form larger concentrations of more easily mined material. Pyrite would be a potential source of iron if these ores should become scarce.

Pyrite has been mined for its sulfur content though. During WWII, sulfur was in demand as a strategic chemical and North American native sulfur mines were drying up. A sulfide deposit near Ducktown Tenn. was found to be able to mine pyrite and other sulfides such as pyrrhotite and pentlandite and produce the needed sulfur as well as iron and other metals. The sulfur was used in the production of sulfuric acid, an important chemical for industrial purposes. Now most sulfur production comes from H2S gas recovered from natural gas wells.

 

PHYSICAL CHARACTERISTICS:

• Color is brassy yellow.
• Luster is metallic.
• Transparency: Crystals are opaque.
• Crystal System is isometric; bar 3 2/m
• Crystal Habits include the cube, octahedron and pyritohedron (a dodecahedron with pentagonal faces) and crystals with combinations of these forms. Good interpenetration twins called iron crosses are rare. Found commonly in nodules. A flattened nodular variety called "Pyrite Suns" or "Pyrite Dollars" is popular in rock shops. Also massive, reniform and replaces other minerals and fossils forming pseudomorphs or copies.
• Cleavage is very indistinct.
• Fracture is conchoidal.
• Hardness is 6 - 6.5
• Specific Gravity is approximately 5.1+ (heavier than average for metallic minerals)
• Streak is greenish black.
• Other Characteristics: Brittle, striations on cubic faces caused by crossing of pyritohedron with cube. (note - striations on cube faces also demonstrate pyrite's lower symmetry). Pyrite unlike gold is not malleable.
• Associated Minerals are quartz, calcite, gold, sphalerite, galena, fluorite and many other minerals. Pyrite is so common it may be quicker to name the unassociated minerals.
• Notable Occurrences include Illinois and Missouri, USA; Peru; Germany; Russia; Spain; and South Africa among many others.
• Best Field Indicators are crystal habit, hardness, streak, luster and brittleness.

 

 

   

THE MINERAL PYROAURITE

 

• Chemistry: Mg₆Fe₂CO₃(OH)₁₆ - 4H₂O, Hydrated Magnesium Iron Carbonate Hydroxide.
• Class: Carbonate.
• Group: Hydrotalcite.
• Uses: Only as mineral specimens.
• Specimens

Pyroaurite is a rare mineral that comes mostly from the famous mines of Langban, Varmland, Sweden, but is also found at a few other localities. It forms platy to tabular crystals. Crystals of pyroaurite can yield flashes of yellow and it is this display that is responsible for its name; which loosely translated means golden fire. Pyroaurite is dimorphous with the mineral sjogrenite. Dimorphs are minerals that share the same chemistry but have different structures.

 

PHYSICAL CHARACTERISTICS:

• Color is usually brownish yellow, reddish brown, yellow, white and greenish brown.
• Luster is vitreous to pearly.
• Transparency: Crystals are usually translucent to transparent.
• Crystal System is trigonal; bar 3 2/m.
• Crystal Habits include tabular, scaley to platy crystals; also found in fibrous forms.
• Cleavage is perfect in one direction (basal).
• Hardness is 2.5.
• Specific Gravity is 2.1 (very light).
• Streak is white.
• Associated Minerals includes hydromagnesite, stitchite, calcite, reevesite, sjogrenite, magnetite and lizardite.
• Notable Occurrences include the type locality of Langban, Varmland, Sweden; Gulsen Quarry, Kraubath, Styria, Austria; Tunnel Hill Quarry, Tasmania, Australia; Sterling Hill, New Jersey; San Francisco County, California, USA; Half-Grunay, Shetland Islands, Scotland; Rutherglan, Ontario and the Parker Mine, Notre Dame du Laus, Quebec, Canada.
• Best Field Indicators are crystal habits, cleavage, color and locality.

 

 

 

 

 

 

THE MINERAL PYROCHLORE

 

• Chemical Formula: (Ca, Na)2Nb2O6(O, OH, F); Calcium Sodium Niobium Oxide Hydroxide Fluoride.
• Class: Oxides and Hydroxides
• Group: Pyrochlore
• Uses: A very minor ore of niobium and rare earth metals and as mineral specimens.
• Specimens

Pyrochlore is one of the tantalum/niobium oxides that are generally difficult to distinguish. Fortunately there are few of them that form exquisitely shaped octahedral crystals. Pyrochlore crystallizes in the isometric symmetry class and forms fine octahedral crystals that are typically and characteristically modified by other isometric forms. Other members of pyrochlore's namesake group the Pyrochlore Group also form octahedrons, but can sometimes be reliably differentiated by color, streak and other characteristics.

Pyrochlore generally contains substantial amounts of radioactive elements called rare earths and this produces the radioactivity in this mineral. It is therefore a member of the informal group of minerals called the Rare Earth Oxides. These minerals are generally difficult to distinguish but the octahedral crystals of pyrochlore once again are usually sufficient indicators.

Pyrochlore is an end member of a solid-solution series between itself and the mineral microlite. The two minerals have similar structures and properties, but microlite is the tantalum rich end member and pyrochlore is the niobium rich end member. The generally lighter pyrochlore is found in a rather unusual igneous rock called a carbonatite (which is composed mostly of calcite) and alkalic pegmatites called nepheline syenites. The overall more common mineral microlite is found mostly in granitic pegmatite dikes and more rarely in the carbonatites. Pyrochlore is the more impure mineral of the two because it is more often accepting of the inclusion of elements such as tantalum, titanium, iron and uranium as well as the previously mentioned rare earth metals into its structure.

Some variety names of pyrochlore are known. "Hatchettolite" and "ellsworthite" both contain uranium and come from the same general location, albeit different mines, in the Hybla area of Hastings County, Ontario, Canada.

Remember, this is a radioactive mineral and should be stored away from other minerals that are subject to damage from radioactivity and of course human exposure should be limited !

 

PHYSICAL CHARACTERISTICS:

• Color is yellow, reddish-brown, red or black.
• Luster can vary from vitreous, adamantine, greasy to resinous.
• Transparency: Crystals are translucent with darker specimens being opaque.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits typically include octahedral crystals that are modified by other isometric forms; also found cubic, granular as disseminated grains and massive.
• Cleavage is in four directions (octahedral), but is indistinct.
• Fracture is conchoidal to uneven.
• Hardness is 5 - 5.5
• Specific Gravity is approximately 3.5 - 4.6 (heavy for non-metallic). Variation caused by extent of inclusion of trace metals into the structure.
• Streak is pale yellow to brown.
• Other Characteristics: Generally radioactive.
• Associated Minerals include calcite, feldspars, apatite, zircon and biotite.
• Notable Occurrences include Veshnovorgorsk, Chelyabinsk Oblast, Russia; Mbeya, Tanzania; St. Peter's Dome, El Paso County, Colorado, USA; Brevik, Norway; Alno, Sweden; Oka, Quebec and Hastings County, Ontario, Canada.
• Best Field Indicators are crystal habit, luster, fracture, color, hardness, radioactivity, associations, environment and specific gravity.

 

    

THE MINERAL PYROLUSITE

 

• Chemical Formula: MnO2, Manganese Oxide
• Class: Oxides and Hydroxides
• Group: Rutile
• Uses: a major ore of manganese and as a mineral specimen
• Specimens

Pyrolusite is the most common manganese mineral and is an important ore. Manganese is a strategically valuable metal since it is an essential ingredient in steel and other alloys. The mining term "wad" is used to indicate ores that are a mixture of several manganese oxides such as pyrolusite, psilomelane and others that are difficult to distinguish.

Pyrolusite is an oxidation product of weathered manganese minerals and also forms from stagnant shallow marine and freshwater bog and swamp deposits. Minerals such as rhodochrosite, rhodonite and hausmannite are often replaced by pyrolusite.

Pyrolusite has some interesting habits dispite its common occurrence as dull, sooty, black masses and/or earthy forms. Possibly its most popular form is its dendritic habit that forms wonderfully detailed, fern-like patterns on the surfaces of rocks such as sandstone. These dendrites are so amazing that they have often been mistaken for fossil plants. Another popular habit is its acicular or hair-like crystal aggregates that produce nice tufts of "hair", or meadows of shiny black pyrolusite fibers. Often specimens of pyrolusite are very difficult to distinguish from other manganese oxides. Thus, as a consequence of its more abundant distribution, pyrolusite is the default name for black, hair-like manganese crystals or powdery black alteration products of manganese minerals in general.

 

PHYSICAL CHARACTERISTICS:

• Color is steel gray to a solid black in earthy specimens.
• Luster is metallic to dull in weather or thinly crusted specimens.
• Transparency crystals are opaque, translucent in only thin splinters.
• Crystal System is tetragonal; 4/m 2/m 2/m
• Crystal Habit is typically massive and compact forms, but also fibrous, acicular, columnar, concretionary, scaly and earthy forms are well known. A thin dendritic habit is commonly seen encrusted on sandstones and siltstones and will form wonderful fern or tree like patterns that are often mistaken for fossil plants. A variety with large, easily visible crystals is called polianite, and occurs as minute prismatic crystals with a square or rectangular cross-section and a wedge-shaped terminations.
• Cleavage is good in two directions forming prisms, but rarely seen except in rare large crystals.
• Fracture is conchoidal to uneven.
• Hardness is 6 in individual crystals, but aggregates can be as soft as 4 or 5 and massive or earthy forms will mark paper and leave powder on fingers (a hardness under 2).
• Specific Gravity is 4.4 - 5.1 (average for metallic minerals)
• Streak is black.
• Associated Minerals are limonite, hematite, quartz, manganite, psilomelane and other manganese and iron oxide minerals.
• Notable Occurances include nice specimens from Germany; iron mines in Minnesota and Michigan and at Lake County, New Mexico, USA. Pyrolusite is mined in many countries around the world with the most productive countries being Georgia and Ukraine of the former USSR, India, China, South Africa, Brazil, Australia and Gabon. Polianite occurs in abundance at the Kisenge Mine, in Zaire.
• Best Field Indicators are habits, luster, softness, color and streak.

 

 

 

 

 

THE MINERAL PYROMORPHITE

 

• Chemistry: Pb5(PO4)3Cl , Lead Chlorophosphate
• Class: Phosphates
• Group: Apatite
• Uses: as a minor ore of lead and mineral specimens
• Specimens

Pyromorphite shares the same structure with apatite and therefore crystals of the two will have similar shapes. Pyromorphite also forms a chemical series with two other minerals; Mimetite (Pb5(AsO4)3Cl) and Vanadinite (Pb5(VO4)3Cl). This series is a little different than most chemical series which involve substitution of cations such as calcium for magnesium. Instead, this series substitutes its basic chemical units the anion groups; phosphate (PO4), arsenate (AsO4) and vanadate (VO4). Green Mimetite or yellow Pyromorphite can make identification between the two difficult, but usually pyromorphite is green and mimetite is yellow. Vanadinite is usually red. Pyromorphite's main characteristic is its unique crystal habit of stacked barrel shaped crystals that branch out in a way that is reminescent of some branching cactus varieties.

 

PHYSICAL CHARACTERISTICS:

• Color is typically green, but can also be yellow, orange and brown.
• Luster is resinous to adamantine.
• Transparency: Crystals are rarely transparent, but usually translucent.
• Crystal System is hexagonal; 6/m
• Crystal Habits include the typical barrel shaped hexagonal prism with the hexagonal pyramid and/or a pinacoid as a termination. A classic specimen of Pyromorphite shows its arborescent habit as described above. Also granular, reniform, encrusting and massive.
• Cleavage is absent.
• Fracture is uneven.
• Hardness is 3.5 - 4.
• Specific Gravity is approximately 7.0+ (very heavy for translucent minerals)
• Streak is off white.
• Associated Minerals are cerussite, limonite, galena and secondary lead deposit minerals.
• Other Characteristics: Index of refraction is 2.05 (typically high for lead minerals) and crystal terminations can be hollowed out or pitted.
• Notable Occurrences include Idaho and Pennsylvania, USA; Mapimi, Mexico; Germany; England and Australia.
• Best Field Indicators are crystal habit, color, lack of transparency and density.

 

     

THE MINERAL PYROPE

 

• Chemistry: Mg3Al2(SiO4)3, Magnesium Aluminum Silicate
• Class: Silicates
• Subclass: Nesosilicates
• Group: Garnets
• Uses: Gemstone and abrasive
• Specimens

Pyrope is the only garnet that is always a shade of red. Although less common than most other garnets, pyrope is a common gemstone. Pyrope is the only garnet whose most common source is igneous rather than metamorphic. Most pyrope comes from ultramafic igneous rocks that contain olivine and/or diamond. Metamorphic pyrope comes from the metamorphism of the igneous rocks previously mentioned or from magnesium rich rocks subjected to high grade metamorphism. Almandine and pyrope form a series in which iron substitutes for the magnesium in pyrope. In fact, pure pyrope is unknown in nature and the various proportions are referred to as pyrope-almandine mixes. one mixture of approximately two to one (pyrope to almandine) is a variety called rhodolite which has an attractive red-lavender color and is cut as a gemstone. Pyrope is difficult to distinguish from almandine but is usually clear and free from flaws, at least more so than almandine.

 

PHYSICAL CHARACTERISTICS:

• Color is red to reddish purple and sometimes a deep enough red to appear black.
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits include the typical rhombic dodecahedron. also seen is the 24 sided trapezohedron. Combinations of these forms are common and sometimes the rare faces of the hexoctahedron, a 48 sided crystal habit that rarely is seen by itself, can also combine with these other forms making very attractive, complex and multifaceted crystals. Massive and granular occurrences are also common.
• Cleavage is absent.
• Fracture is conchoidal.
• Hardness is 7 - 7.5
• Specific Gravity is approximately 3.6 (above average for translucent minerals)
• Streak is white.
• Associated Minerals are olivine, serpentine, biotite, hornblende, augite, pyroxenes and diamond.
• Other Characteristics: index of refraction is 1.73
• Notable Occurrences include localities in Europe; Arizona and New Mexico, USA; South Africa and several Australian sites.
• Best Field Indicators are crystal habit, color, hardness and enviroment.

 

 

THE MINERAL PYROPHYLLITE

 

• Chemistry: AlSi2O5OH , Aluminum Silicate Hydroxide.
• Class: Silicates
• Subclass: Phyllosilicates
• Group: The Clays
• Uses: As a refractory mineral, as a filler for rubber, paints and insecticides, as an ornamental stone, as a component of ceramics and as mineral specimens.
• Specimens

Pyrophyllite is an early stage metamorphic mineral and is actually quite common although usually not very abundant as good mineral specimens. It is found as a constituent of slate, phyllite (which is not named after pyrophyllite), some schists and other early stage metamorphic rocks. It is most common in the phyllites were its pearly luster helps give the phyllites their well known shiny luster. Other minerals that contribute to the luster of phyllite include the micas, sericite, chlorite, graphite, quartz and epidote.

Pyrophyllite gets its name from the Greek words for fire and leaf as in "fire-leaf". Phyllite is named after the Greek word for leaf as well, in allusion to its flaky fracture. But pyrophyllite gets its name from the fact that it exfoliates when water is driven off upon heating, leaving a flaky mass. The flakes are actually the silicate sheets that are a testament to pyrophyllite's structure.

Pyrophyllite is a member of the phyllosilicates, or "leaf" silicates, which have a sheet-like structure. The phyllosilicates form stacks of silicate layers that are composed of SiO4 tetrahedrons. The sheets are not directly linked above or below to the next silicate sheets.

In pyrophyllite, two silicate layers are sandwiched in between the so called gibbsite layer. Gibbsite, AL(OH)3, is its own mineral and is composed of octahedrally coordinated aluminums surrounded by six hydroxides. The gibbsite layer (G) in pyrophyllite is identical to gibbsite's structure except that four of the hydroxides are replaced by four oxygens from the silicate layers (S). The overall structure of pyrophyllite can be imagined as stacked S-G-S sandwiches. The bonding between these sandwiches is nearly nonexistent and gives rise to pyrophyllite's softness and perfect cleavage.

There are actually two pyrophyllite minerals. One is monoclinic and the other triclinic. Ordinarily they would be treated as two distinct minerals, but their properties are identical and they are often associated and intergrown. Separating them serves no purpose and the two minerals are often considered as one; at least for now.

Pyrophyllite is also identical in physical properties to a quite distinct mineral called talc. The two are isomorphous, meaning they share the same monoclinic structure but have different chemistries. Talc has magnesiums instead of aluminums and is basically indistinguishable from pyrophyllite without a chemical test for aluminum. The test for aluminum involves applying a slight amount of cobalt nitrate solution on the specimen and then igniting the solution. The specimen should change color; a blue color confirms pyrophyllite, a violet color confirms talc.

A variety of pyrophyllite is called "agalmatolite and is used by Chinese artisans as an ornamental stone. Although pyrophyllite loses water and exfoliates, at higher temperatures it is quite stable up to 800 degrees C. This makes pyrophyllite valuable as a refractory mineral and for other applications. Pyrophyllite shares many of the same purposes as talc although it is usually considered inferior to the better grades of talc in all but one use. Pyrophyllite seems to be best as a carrier for insecticides and is often the filler for these products.

Although an ordinary metamorphic mineral in most regards, pyrophyllite is still quite interesting and does form some very attractive mineral specimens. The radiating stellate aggregates that come from Mariposa County, California and North Carolina for example are quite appealing with their bright pearly luster and radiating habit.

 

PHYSICAL CHARACTERISTICS:

• Color is usually white, colorless, gray, yellow, pale green and/or blue. It can also be stained brown by iron oxides.
• Luster is greasy to dull, but pearly on cleavage surfaces.
• Transparency: Crystals are mostly translucent to opaque.
• Crystal System is monoclinic; 2/m and triclinic; bar 1.
• Crystal Habits include the typical fine grained, fibrous and lamellar masses, stellate aggregates and radiating spherules. Individual crystals are rare, but usually have a tabular subhedral or distorted form.
• Cleavage is perfect in one direction.
• Fracture is uneven or splintery.
• Hardness is 1 - 1.5 (soft enough to be scratched by a fingernail).
• Specific Gravity is approximately 2.65 - 2.85 (average).
• Streak is white.
• Other Characteristics: Cleavage sheets are flexible, but inelastic. A distinctive greasy feel to the touch.
• Associated Minerals: are numerous, but a short list would include the micas, sericite, chlorite, graphite, quartz, albite, barite, gypsum, andalusite, kyanite, sillimanite, lazulite and epidote.
• Notable Occurrences include Randolph, Guilford and Orange Counties, North Carolina, Chesterfield County, South Carolina; Mariposa County and San Bernardino County, California, Arizona and Graves Mountain, Georgia, USA as well as Belgium; China; Switzerland; Mexico; Minas Gerais, Brazil; Sweden; Ural Mountains, Russia; Korea and Japan.
• Best Field Indicators are crystal habit, color, cleavage, softness, aluminum test and feel.

 

THE MINERAL PYRRHOTITE

 

• Chemistry: Fe1-xS (x=0 to x=0.2), Iron Sulfide
• Class: Sulfides and Sulfosalts
• Group: Nickeline
• Uses: mineral specimens and as an ore of sulfur and iron.
• Specimens

Pyrrhotite has some unusual characteristics. First, it has an unusual formula. The amount of sulfur does vary by roughly 20% or 50 to 55 atoms of sulfur per 50 atoms of iron. Or is it the iron that varies? Really the same difference. Thus the unusual formula of Fe1-xS.

Secondly, it has two symmetries. While this should indicate that there are two minerals and not one, in the case of pyrrhotite, mineralogists have made an exception. When pyrrhotite is low in sulfur and the formula is closer to true FeS, then the structure is hexagonal. But when it is high in sulfur, the structure is monoclinic. Clearly two different symmetries, two different formulae; therefore, two different minerals . . . except, that in natural pyrrhotite crystals both phases are present in the same crystal. If you are a purist, you can think of a pyrrhotite crystal as an assemblage of two minerals, but most minerologists treat it as one.

Thirdly, pyrrhotite is magnetic or at least weakly so. It is the next most common magnetic mineral to magnetite. Although not all specimens will show great evidence of magnetism if any, some will attract a paperclip or needle suspended from a string or move the needle of a compass. Massive pyrrhotite is common and magnetism is sometimes the only way to distinguish it from other brassy colored sulfides such as chalcopyrite, pyrite, pentlandite or marcasite Good crystals are rare and should rightly be treasured as comming from a very unusual mineral.

 

PHYSICAL CHARACTERISTICS:

• Color is bronze.
• Luster is metallic.
• Transparency crystals are opaque.
• Crystal System hexagonal, 6/m2/m2/m and monoclinic; 2/m
• Crystal Habits: tabular or prismatic in hexagonal prisms with a pinacoidal termination, but mostly massive rock forming beds with other sulfides.
• Cleavage none but there is a strong parting tendency.
• Fracture is uneven
• Hardness is 3.5-4.5
• Specific Gravity is 4.6
• Streak gray-black
• Associated Minerals pentlandite, quartz, ankerite, pyrite and other sulfides.
• Other Characteristics: weakly magnetic, prism faces striated parallel to pinacoid faces and color will darken with exposure to light.
• Notable Occurances Sudbury, Ontario; Ducktown, Tennessee; Chihuahua, Mexico; Russia; Germany and Brazil.
• Best Field Indicators magnetism, crystal habit, hardness and color.