Thursday, August 18, 2011

Mineral E


 

 

 

THE MINERAL EDENITE

 


Edenite is an uncommon amphibole mineral. It is related to the more well known amphibole, hornblende. Although hornblende is no longer an official mineral, it still serves as a general name for iron, magnesium, aluminum and calcium rich amphiboles of which edenite is one. Edenite had been referred to as "edenitic hornblende" before the name edenite was officially adopted as an official and distinct mineral.

Edenite is placed in the Tremolite Subgroup of the Amphibole Group. It is interesting to compare edenite to the more common tremolite; Ca2Mg5Si8O22(OH)2. A close look at the formulas of the two minerals shows that edenite contains both a sodium atom and an aluminum atom that is lacking in tremolite (as well as some iron). To compensate, tremolite has an extra silicon. This helps to illustrate edenite's environment of formation which tends to be sodium and aluminum rich granitic pegmatites and metamorphic skarns.

Edenite has a close cousin called ferro-edenite; NaCa2(Fe, Mg)5AlSi7O22(OH)2. The two minerals form a solid solution series in which the iron and magnesium substitute for each other. Ferro-edenite is the iron rich member hence the ferro designation, while edenite is the magnesium rich member. Edenite's formula is often written without the iron content implying a pure contentration of magnesium, but iron is almost always present in edenite.

Edenite was discovered in the 1830's while ferro-edenite was not discovered until the 1940's. Edenite was discovered in the rocks of the Franklin Marble, a formation that extends from the famous mines of Franklin, New Jersey into New York. Edenite gets its name from Edenville, New York, its type locality. Another similar mineral to edenite has been proposed called fluoro-edenite which is the same as edenite but fluorines would replace the hydroxides.

Edenite can form nice, well formed and sometimes complex monclinic crystals. Its translucent green specimens provide for the best examples of this species. Although not common, edenite is found around the world. It is unfortunately easily confused with other amphibole minerals such as tremolite, hornblende and fluorrichterite. Misidentification is a problem for this species as it has been identified from several localities only to have those specimens later attributed to other amphiboles, sometimes years later. Or possibly not recognized at first, only to be confirmed later if at all. Edenite is quite possibly more widespread than currently believed.

 

PHYSICAL CHARACTERISTICS:

  • Color is green to black also dull gray or brown.
  • Luster is vitreous to pearly to dull.
  • Transparency: Crystals are generally translucent to opaque.
  • Crystal System is Monoclinic; 2/m
  • Crystal Habits include prismatic to stubby crystals with a nearly diamond shaped cross-section the points of which can be truncated by minor prism faces. The typical termination appears to be the two faces of a slightly slanted dome but is actually two of the four faces of a prism. The termination faces are not only slanted toward each other but the two faces are slanted with respect to the long axis of the crystal as well. Some terminations are rather complex and can make the crystal appear pseudo-orthorhombic. Twinning is commonly seen and results in a groove or notch running down the "spine" of the prismatic crystals. A fibrous habit is also seen.
  • Cleavage is imperfect in two directions at nearly 60 and 120 degrees.
  • Fracture is uneven.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 3.06 (slightly above average for non-metallic minerals)
  • Streak is white.
  • Associated Minerals include tremolite, kaolinite, biotite, pyroxenes, spinel and calcite.
  • Notable Occurrences include the type locality of Edenville, Orange County, New York, USA as well as Mont Saint-Hilaire, Quebec, Canada; Franklin, New Jersey, USA; Cygnet, Tasmania, Australia; England and Aldan Shield, Siberia, Russia.
  • Best Field Indicators are crystal habit (especially cross-section), color, luster, locality and cleavage.

 

 

 

 

THE MINERAL EDINGTONITE

 


Edingtonite is another example of the variety offered in the Zeolite Group of minerals. Like so many other zeolites, it is not a surprise to see that edingtonite is typically found in the cavities of volcanic rocks. Although not a colorful mineral, it does form some nice well-shaped crystals. It is an unusual mineral in that it has two polytypes or two phases that are not yet recognized as separate minerals. One type has a little more water content and a has an orthorhombic symmetry. The other type has a tetragonal symmetry. Both types have an overall tetragonal look to their crystals.

Edingtonite's structure has a typical zeolite openness 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 edingtonite can act as a chemical sieve, allowing some ions to pass through while blocking others.
Edingtonite is one of only two zeolites to have barium in its chemistry. The other one is harmotome, with a formula of BaAl2Si6O16 - 6H2O. The heavy barium ion gives edingtonite the highest density of any zeolite. The larger amounts of water and the lower barium ion ratio lowers harmotome's density in relation to edingtonite.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white.
  • Luster is vitreous to dull.
  • Transparency: Crystals can be transparent but most commonly are just translucent.
  • Crystal System is tetragonal and orthorhombic.
  • Crystal Habits include blocky to prismatic or bladed crystals usually with a square cross-section, also massive.
  • Cleavage is perfect in one direction lengthwise.
  • Fracture is uneven.
  • Hardness is 4
  • Specific Gravity is approximately 2.8 (average, although heavy for a zeolite).
  • Streak is white.
  • Associated Minerals are manganite, heulandite, natrolite, stilbite and other zeolites.
  • Notable Occurrences include Ice River, Canada; Old Kilpatrick, Scotland and Bohlet, Sweden.
  • Best Field Indicators are crystal habit, density and associations.

 

 

 

THE MINERAL ELPIDITE

 


Elpidite is another in the long list of unusual mineral that come from agpaitic pegmatite rocks. Agpaitic pegmatite intrusions are unusual igneous rocks that are high in alkaline metals (such as sodium) and poor in silica. These intrusions also contain a large number of unusual elements such as zirconium. Elpidite was first discovered at Narsarsuk, Greenland, from where the first specimens were described in 1932. It is also found at Mont Saint-Hilaire, Quebec; another agpaitic pegmatite location. Mont Saint-Hilaire is undoubtedly the best location for elpidite specimens, as specimens from there form large sprays and interesting aggregates; and some specimens are fluorescent. Elpidite is a rare zirconium silicate mineral that can have a very nice crystal form and provide good specimens for micromounts and even larger cabinet specimens.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white, gray, tan to brick-red.
  • Luster is vitreous, earthy, dull or silky.
  • Transparency: Crystals are typically opaque to translucent or rarely transparent.
  • Crystal System is orthorhombic.
  • Crystal Habits include prismatic or acicular crystals often forming sprays or stibnite-like aggregates. Individual crystals can have sharp pointed terminations
  • Cleavage is good in two directions (prismatic).
  • Fracture is splintery or uneven.
  • Hardness is variable at 5 - 7.
  • Specific Gravity is approximately 2.5 to 2.6
  • Streak is white.
  • Other Characteristics: some specimens fluoresce green or yellow-green under shortwave UV light.
  • Associated Minerals are calcite, albite, bastnasite, apatite, rutile, pyrochlore, siderite, epididymite, chlorites, natrolite and aegirine.
  • Notable Occurrences include the type locality at Narsarsuk, Julianehaab district, Greenland and perhaps the best source for collection specimens is Mont Saint-Hilaire, Quebec, Canada. Also found at Langesundfjord, Norway.
  • Best Field Indicators: Crystal habit, color, cleavage, associations and localities.

 

 

 

 EMERALD,

the green variety of beryl


VARIETY INFORMATION:

  • VARIETY OF: Beryl , Be3 Al2 Si6 O18 .
  • USES: Gemstone.
  • BIRTHSTONE FOR: May
  • COLOR: various shades of green.
  • INDEX OF REFRACTION: 1.57 - 1.60
  • BIREFRINGENCE: 0.004 - 0.008
  • HARDNESS: 7.5 - 8
  • CLEAVAGE: one direction, poor.
  • CRYSTAL SYSTEM: hexagonal
  • Pleochroic: weak
  • For natural emerald mineral specimens see our For Sale or Sold lists

Emerald is the green variety of the mineral beryl. Other gemstone color varieties that belong to beryl include aquamarine, morganite, and heliodor. Other colors of beryl are simply refered to by their color, such as red beryl.

The wonderful green color of emerald is unparalleled in the gem kingdom. Emerald's precious green color is caused by small amounts of chromium and enhanced by traces of iron. Unlike other beryls, emeralds often contain inclusions and other flaws. These flaws are not looked on as negative aspects for emerald like they would be for other gemstones. Indeed, these flaws are considered part of the character of the stone and are used to assure the purchaser of a natural stone.

 

 

 

 

THE MINERAL ENARGITE

 

  • Chemistry: Cu3AsS4, Copper Arsenic Sulfide
  • Class: Sulfides
  • Subclass: Sulfosalts
  • Uses: As a minor ore of copper and as mineral specimens.
  • Specimens

Enargite is a somewhat rare copper mineral. It does not often form well shaped crystals, but there are several localities that produce some fine enargite clusters. Its crystals that form tabular to blocky to prismatic forms are often pseudohexagonal, having six sides but not six identical sides. Twinning is common for enargite and can form a nice star shaped cyclic twin called a trilling.

Enargite is related to the rare mineral wurtzite. Wurtzite is a zinc sulfide with a formula of ZnS. In enargite 75% of the zinc atoms are replaced by copper and 25% of the zinc atoms are replaced by arsenic, Cu3AsS4. The similarity is easier to see if wurtzite's formula is rewritten as Zn4S4. The different elements however do not lend themselves to the exact same structure as wurtzite has a symmetry of hexagonal; 6 m m and enargite's symmetry is orthorhombic; 2 m m.

The symmetry of enargite is very uncommon. It belongs to a symmetry class that produced hemimorphic crystals and is typified by the mineral hemimorphite. The hemi means half while the morph means shape. General hemimorphic crystals can have differently shaped tops compared to the bottoms of the crystals. In enargite, the crystals do not have any unique terminations, just a flat face. The "bottom" of the crystals would have a flat face as well, but how do you tell one flat face from another? In the mineral hemimorphite, the top termination faces slant to a point and the bottom termination is much more blunted, a clear difference. Unfortunately for enargite its hemimorphic character is undetectable because of its crystal form.

 

PHYSICAL CHARACTERISTICS:

  • Color is gray to black.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2 m m
  • Crystal Habits include pseudohexagonal prismatic to blocky or tabular crystals, often terminated by a flat pedion face. Also found massive, granular and in radiating aggregates. Twinning is common and sometimes results in a star shaped cyclic twin called a trilling.
  • Cleavage is perfect in two directions, prismatically; distinct in two other directions also prismatically but with different orientations.
  • Fracture is uneven.
  • Hardness is 3 - 3.5
  • Specific Gravity is approximately 4.4+ (average for metallic minerals)
  • Streak is black.
  • Other Characteristics: crystals are typically striated lengthwise and a tarnish will dull the luster of crystals over time.
  • Associated Minerals are quartz, bornite, galena, sphalerite, tennantite, chalcocite, chalcopyrite, covellite, pyrite and other sulfides.
  • Notable Occurrences include Butte, Montana, San Juan Mountains, Colorado and at both Bingham Canyon and Tintic, Utah, USA; Sonora, Mexico; Argentina; Chile; Morococha and Cerro de Pasco, Peru and Island of Luzon, Philippines.
  • Best Field Indicators are crystal habit, streak, cleavage and associations.

 

 

 

 

THE MINERAL ENSTATITE

 


Enstatite is a relatively common mineral and is found in metamorphic and some igneous rocks as well as in stony and iron meteorites. It forms a solid solution series with the minerals hypersthene and ferrosilite. A solid solution series occurs when two or more elements can substitute for each other in a crystal structure without much alteration of the structure. In this case, the elements are iron and magnesium and enstatite is the magnesium end member of the series. Hypersthene is the intermediate member with around 50% iron and ferrosilite is the iron rich end member of the series. Hypersthene is fairly common but ferrosilite is extremely rare. The iron deeply colors the minerals and therefore any deeply colored specimens of this series are usually called hypersthene. In fact the two most common members of the series are often considered together as enstatite-hypersthene in many mineral guides and texts.

Enstatite is an orthopyroxene or a pyroxene with an orthorhombic symmetry. At high temperatures, enstatite's structure changes to a structure with a monoclinic symmetry, a clinopyroxene or more specifically, clinoenstatite. Clinoenstatite is a polymorph of enstatite, meaning that it has the same chemistry but a different structure.

Enstatite has a couple of ornamental and gemstone varieties. A weathered variety that has a submetallic luster and a bronze like color is called "bronzite". It is sometimes used as an ornamental stone. Both enstatite and hypersthene contribute to the bronzite variety. An emerald green variety of enstatite is called chrome-enstatite and is cut as a gemstone. The green color is caused by traces of chromium, hence the varietal name.

Enstatite would form more commonly in igneous rocks if it were not for the abundance of iron in most magmas. As a result, enstatite is more commonly seen in highly metamorphosed rocks called granulites. It commonly forms from the alteration and de-watering of the amphibole mineral anthophyllite, (Mg, Fe)7Si8O22(OH)2.

 

 

PHYSICAL CHARACTERISTICS:

  • Color is typically white, colorless, gray, light brown or pale green.
  • Luster is vitreous to pearly. Weathered specimens can have a submetallic luster ("bronzite").
  • Transparency: Crystals are generally translucent and rarely transparent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include rare individual crystals that have a stubby prismatic habit. More typically massive or in coarse lamellar or fibrous aggregates.
  • Cleavage is perfect in two directions at nearly 90 degrees.
  • Fracture is conchoidal.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 3.2+ (slightly above average for translucent minerals)
  • Streak is white.
  • Other Characteristics: Index of refraction is approximately 1.65.
  • Associated Minerals include iron and stony meteorites, augite, feldspars and certain types of garnets.
  • Notable Occurrences include the Tilly Foster Mine, Brewster, New York; Boulder, Colorado; Jackson Co., North Carolina; Lancaster Co., Pennsylvania and Bare Hills, Maryland, USA as well as many localities from around the world especially in India, Burma and Tanzania.
  • Best Field Indicators are color, crystal habit, hardness, cleavage, index of refraction and luster.

 

 

 

THE MINERAL EOSPHORITE

 

  • Chemistry: (Mn, Fe)AlPO4(OH)2 - H2O, Hydrated Manganese Iron Aluminum Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens

Eosphorite is a somewhat common secondary mineral. It forms from the alteration of primary granitic phosphates such as lithiophilite and triphylite when aluminum and water are available. Eosphorite has been made famous in the mineral collecting world by being an accessory to the wonderfully well formed crystals of rose quartz at Taquaral, Minas Gerais, Brazil.

Eosphorite forms a solid solution series with the mineral childrenite. Childrenite's formula is (Fe, Mn)AlPO4(OH)2 - H2O and differs from eosphorite by being rich in iron instead of manganese. The structures of the two minerals are the same and therefore it would be expected that their differences in physical properties between the two would be related to the iron/manganese percentage. Eosphorite is less dense and is generally pinkish to rose-red in color whereas childrenite's colors tends towards various shades of brown. In terms of crystal habits the two also differ. Eosphorite forms prismatic, slender crystals and rosettes. Childrenite forms tabular or bladed individuals or lamellar aggregates. It has been said that the two different habits belie their solid solution relationship.

 

PHYSICAL CHARACTERISTICS:

  • Color is varied with colors of pink, salmon-pink, yellow, colorless, red and even brown or black.
  • Luster is vitreous.
  • Transparency: Specimens are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include prismatic slender crystals and radial aggregate sprays. Crystals are usually altered or partially dissolved.
  • Cleavage is good in two directions at right angles.
  • Fracture is conchoidal.
  • Hardness is 5.
  • Specific Gravity is approximately 3.0 (average), but increases with increased iron content.
  • Streak is white.
  • Associated Minerals include rose quartz, lithiophilite, hureaulite and triphylite.
  • Notable Occurrences include Taquaral, Minas Gerais, Brazil; Hagendorf, Bavaria, Germany; White Picacho district, Arizona; Branchville, Connecticut; Mt. Mica, Maine and the Palermo Mine, New Hampshire, USA.
  • Best Field Indicators are crystal habit, color, associations, localities and density.

 

 

 

THE MINERAL EPIDIDYMITE


Epididymite is yet another classic mineral from agpaites. An unusual igneous intrusive rock that is similar to nepheline-syenites. These rocks are enriched in alkali metals and exotic elements and conversely low in aluminum and silica. Sodium is the chief alkali metal that is present in agpaites and so it is no surprise it is found in epididymite. The beryllium is one of those exotic elements that are in unusual concentrations in agpaites and thus allow minerals like epididymite to form. It is the collector that is rewarded by these unusual rare mineral producing rocks and agpaite deposits are always on the "locality radar" of mineral collectors. Epididymite's locality list is the Who's Who of agpaitic sites. Places like Kola Peninsula, Russia; Mont Saint-Hilaire, Canada; Langesundfjord, Norway and Narssarssuk, Greenland are all top sites for these rare silicate minerals.

Epididymite forms a wide range of habits and this can lead to confusion in identification. Its most popular habit, which makes for easy identification, is its twin. It forms six sided tabular trillings similar to the classic aragonite twins. The twins are usually cloudy but they are generally well formed. Also fishtail twins are quite interesting as well.
Epididymite gets its name from the Greek words for "near" - epi and "twin" - didymus in allusion to its "near twin", eudidymite. Epididymite and eudidymite are not twins, but dimorphs! Dimorphous minerals are minerals that share the same chemistry, but have different structures. Epididymite's structure is orthorhombic and eudidymite's structure is monoclinic, symmetrically speaking. The best known dimorphs are diamond, (symmetry: Isometric) and graphite, (symmetry: Hexagonal) both of which are made of just carbon.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually white or colorless, but can be pale gray, blue, yellow or violet.
  • Luster is vitreous to silky.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is orthorhombic.
  • Crystal Habits include fibrous, acicular and prismatic habits, but more commonly found as tabular, somewhat elongated crystals and aggregate spherulites. Twinning is frequently seen as six sided tabular to columnar trillings and "fishtail" twins.
  • Cleavage: is perfect in two directions (basal and prismatic).
  • Fracture is splintery to uneven.
  • Hardness is 6 - 7.
  • Specific Gravity is approximately 2.5 - 2.6 (average for translucent minerals).
  • Streak is white.
  • Associated Minerals are many and include nepheline, aegirine, pyrite, sphalerite, serandite, eudialyte, catapleiite, elpidite, pyrophanite, astrophyllite, molybdenite, natrolite, siderite, rhodochrosite, calcite, analcime, feldspars, micas and fluorite.
  • Notable Occurrences include Kola Peninsula, Russia; Mont Saint-Hilaire, Quebec, Canada; Langesundfjord, Norway and Narssarssuk, Greenland.
  • Best Field Indicators are crystal habit, cleavage, associations, locality and hardness.

 

 

 

 

THE MINERAL EPIDOTE

 

  • Chemistry: Ca2(Al, Fe)3(SiO4)3(OH), Calcium Aluminum Iron Silicate Hydroxide.
  • Class: Silicates
  • Subclass: Sorosilicates
  • Group: Epidote
  • Uses: mineral specimens and rarely as a gemstone.
  • Specimens

Epidote is a structurally complex mineral having both single silicate tetrahedrons, SiO4, and double silicate tetrahedrons, Si2O7. The formula of epidote could be expressed in a such a way so as to reflect this organization; Ca2(Al, Fe)Al2O(SiO4)(Si2O7)(OH). The two aluminums represent the parallel chains of AlO6 and AlO4(OH)2 octahedra that are the heart of the epidote structure. The silicate groups and extra ions connect the chains together. Since the chains are parallel, the crystals tend to be prismatic. The chains are arranged in parallel planes and the perfect cleavage breaks the bonds between these planes. Epidote, while not general known for exceptional crystals can produce some magnificent specimens. Its unique green color which is often described as "pistachio", is quite striking in well colored specimens.

 

PHYSICAL CHARACTERISTICS:

  • Color is "pistachio" green to yellowish or brownish green, also brown to black.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System monoclinic; 2/m
  • Crystal Habits include long, somewhat prismatic or tabular crystals with a typically dominant pinacoid that the crystal is often flattened against. The terminations are wedge shaped or tappered pyramids. Many clusters show grooved slender crystals or acicular sprays. Also massive, fiberous or granular.
  • Cleavage good in one direction lengthwise.
  • Fracture is uneven to conchoidal.
  • Hardness is 6-7
  • Specific Gravity is 3.3-3.5
  • Streak white to gray
  • Associated Minerals calcite, biotite, hornblende, actinolite, andradite garnet and other metamorphic minerals.
  • Other Characteristics: striated to the depth of grooves in some crystals.
  • Notable Occurances Untersulzbachtal, Austria; Italy; Baja, Mexico and many localities in the USA.
  • Best Field Indicators only one direction of cleavage, crystal habit, color and hardness.

 

 

 

 

THE MINERAL EPISTILBITE

 


Epistilbite is one of the rarer zeolites, a popular group of minerals to collect. Epistilbite commonly forms in the petrified bubbles (called vesicles) of volcanic rocks that have had a slight amount of exposure to metamorphism. It also forms in some pegmatites. Epistilbite's name means over stilbite perhaps in allusion to crystals of epistilbite that form over crystals of stilbite, a closely related zeolite. Epistilbite has similar crystal habits to stilbite although it rarely forms the large, impressive clusters that has made stilbite so famous.

Epistilbite's structure has a typical zeolite openness 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 epistilbite can act as a chemical sieve, allowing some ions to pass through while blocking others.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white, pink and reddish.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include tabular to prismatic crystals, sometimes fibrous and radiating. Twinning is common with the interpenetration twin forming a cruciform (cross) shaped crystal.
  • Cleavage is perfect in one direction.
  • Fracture is uneven.
  • Hardness is 4.
  • Specific Gravity is approximately 2.2 - 2.3 (very light)
  • Streak is white.
  • Associated Minerals are quartz, beryl, calcite, yugawaralite, heulandite, stilbite and other zeolites.
  • Notable Occurrences include Poona, India; Berufjord, Iceland; Osilo, Sardinia, Italy; Isle of Skye, Scotland and in pegamtites at Bedford, New York and in the basalts of Hawaii, USA
  • Best Field Indicators are crystal habit, low density, locality and associations.

 

 

 

 

THE MINERAL EPSOMITE

 

  • Chemistry: MgSO4 - 7H2O, Hydrated Magnesium Sulfate.
  • Class: Sulfates
  • Uses: A source of magnesium salts, various chemical and medicinal uses and as mineral specimens.
  • Specimens

Epsomite, or heptahydrite as it is known in chemistry circles, is one of only a few water soluble sulfate minerals. It is actually well known in most households as the artificially created epsom salt. Magnesium sulfate's medicinal uses were discovered from mineral waters at Epsom, England from where epsom salt and epsomite get their names.

Epsomite forms from as an efflorescent (a precipitation from vapors), on limestone cave walls and on the walls and timbers of various mines. It has been found in deposits from hot springs and fumaroles such as on Mt. Vesuvius, Italy. Epsomite forms large sedimentary beds having been included in some very unusual marine salt deposits in South Africa.
As might be expected, large crystals are few. Crusts and massive forms are more common. Some of the best specimens have attractive fibrous almost cotton-like aggregates with a silky luster.
Identification is usually pretty easy. Besides the easy solubility, the taste is very diagnostic. If you have ever tasted epsom salt, you have tasted epsomite and know of the bitter taste.

The easy solubility is a detriment to most specimens in collections. To keep epsomite it is recommended to clean the specimens gently with alcohol and then store them in sealed containers. In dry air conditions, epsomite may lose one molecule of water and convert to the very closely related mineral hexahydrite, MgSO4 - 6H2O. It is perhaps hard to believe that the loss of one molecule of water can make a new mineral, but in this case the water molecules are intricately involved with the structure of epsomite. This is seen in the change of symmetry from orthorhombic in epsomite to monoclinic in hexahydrite.

The symmetry of epsomite happens to be rather notable. It is one of the very few minerals that crystallize in the Orthorhombic Disphenoidal Class. This symmetry class has just three 2 fold rotational axes at right angles to each other. No mirror planes or other symmetry operations. It is unfortunate that epsomite does not typically form well shaped crystals that show the unusual symmetry.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless, white with pale shades of pink and green.
  • Luster is vitreous in large crystals; silky to earthy in most specimens.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System is orthorhombic; 2 2 2.
  • Crystal Habits include fibrous, acicular, encrusting, stalactitic, botryoidal and granular masses. Typically formed on the walls of caves and mines as efflorescences and in playa lakes.
  • Cleavage is perfect in one direction and distinct in two other directions.
  • Fracture is conchoidal.
  • Hardness is 2 - 2.5
  • Specific Gravity is approximately 1.7 (well below average).
  • Streak is white to colorless.
  • Other Characteristics: Is very soluble in water. A fact that is a detriment to most collection specimens as they may absorb water from the air and deteriorate over time. The taste is bitter like epsom salt.
  • Associated Minerals include aragonite, gypsum, calcite , mirabilite, pyrite and pyrrhotite.
  • Notable Occurrences include Epsom (hence the name), Surrey, England; Mt. Vesuvius, Italy; Stassfurt, Germany; Herault, France; Kruger Mountain, Oroville, Washington; Albany County, Wyoming; El Tiro Mine, Arizona and Carlsbad, New Mexico, USA; Ashcroft, British Columbia, Canada and South Africa.
  • Best Field Indicators are crystal habit, low density, associations, solubility in water and taste.

 

 

 

 

 

THE MINERAL ERIONITE

 

  • Chemistry: approximately (K2, Na2, Ca)MgAl8Si28O72 - 28H2O, Hydrated Potassium Sodium Calcium Magnesium Aluminum Silicate
  • Class: Silicates
  • Subclass: Tectosilicates
  • Group: Zeolites
  • Uses: Mineral specimen and chemical filter.
  • Specimens

Erionite is one of the rarer zeolites, a popular group of minerals to collect. Erionite has been challenged as a new mineral species. It was thought to be another rare zeolite named offretite. Offretite was named first and if erionite were proven in actuality to be offreite then offretite would have priority. First named gets priority in the mineral naming business. There is still some discussion on this matter in mineral parlance.

Erionite forms wool-like, fibrous masses in the hollows of rhyolitic tuffs and in basalts. The form is such that hardness measurements are impossible and basically irrelevant. The crystals not only look like wool they feel like wool as well. But they are brittle and stroking a specimen of erionite is a good way to ruin a specimen erionite, (see okenite).

Erionite's structure has a typical zeolite openness 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 erionite can act as a chemical sieve, allowing some ions to pass through while blocking others.

 

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is hexagonal.
  • Crystal Habits is limited to wool-like aggregates and crusts.
  • Hardness is unknown.
  • Specific Gravity is approximately 2.0 (very light)
  • Streak is white.
  • Associated Minerals are opal, calcite, heulandite, clinoptilolite, pyrite, thenardite, halite, celandonite, herschelite, phillipsite, chabazite, analcime and other zeolites.
  • Notable Occurrences include Durkee, Baker County, Oregon; Nevada, South Dakota and Arizona, USA and the Faroe Islands.
  • Best Field Indicators are crystal habit, low density, locality and associations.




 

THE MINERAL ERYTHRITE

 

  • Chemistry: Co3(AsO4)2-8(H2O) , Hydrated Cobalt Arsenate
  • Class: Phosphates
  • Group: Vivianite
  • Uses: a very minor ore of cobalt and mineral specimens
  • Specimens

Erythrite is a wonderful mineral for people who like striking, unusual colors. Its characteristic bright red-purple color is very noticable and was used to spot veins of cobalt-bearing ore. Erythrite, or "Cobalt Bloom" as it is called by miners, is a weathering product of cobalt-containing minerals such as cobaltite. Where weathered cobalt and nickel ores are found, both annabergite, Ni3(AsO4)2-8(H2O) and erythrite become important markers. Annabergite, called "Nickel Bloom", is bright green and is isostructural with erythrite. "Isostructural" means that the two minerals have the same structure but different chemistries. The two minerals are actually in a series where the nickel and cobalt ions can substitute freely for each other. When the two ions are in near-equal concentrations the resulting color is gray or off-white. A third mineral is also isostructural with erythrite and is called kottigite or koettigite, Zn3(AsO4)2-8(H2O). However, the series is incomplete, meaning that the zinc and cobalt ions only substitute for each other on a very limited basis. Most erythrite is found in the form of crusts, but specimens from Morocco have larger crystals. The unique red-purple color of erythrite is very attractive, and its nice sparkle make this mineral a joy to add to one's collection.

 

PHYSICAL CHARACTERISTICS:

  • Color is deep red-purple to lighter pinks in massive and thin crust forms.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include flattened, striated blades or radiating accicular crystals; crystals are rare. More commonly as crusts or earthy masses.
  • Cleavage is perfect in one direction.
  • Fracture is uneven
  • Hardness is 1.5 - 2.5
  • Specific Gravity is approximately 3.1 (average for translucent minerals)
  • Streak is pale red.
  • Associated Minerals are silver, cobaltite, skutterudite, and other cobalt vein minerals.
  • Other Characteristics: blades are flexible and sectile.
  • Notable Occurences include Cobalt, Ontario; Bou Azzer, Morocco and Germany.
  • Best Field Indicators are color, associations and flexible crystals.

 

 

 

 

THE MINERAL ESPERITE

 

  • Chemistry: Ca3PbZn4(SiO4)4 , Calcium Lead Zinc Silicate.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Group: Trimerite
  • Uses: A very minor ore of zinc and as mineral specimens.
  • Specimens

Esperite is one of the 70 some fluorescent minerals from Franklin and Sterling Hill, New Jersey. It will fluoresce a nice yellow color under short-wave ultraviolet light. This fluorescent color is in striking contrast to the normal color of esperite. Under normal light, esperite is white or colorless. Fluorescence occurs when the ultraviolet light (invisible to humans) imparts energy to some of the atoms in the mineral. This energy is converted by the atom into visible light that we can then see. The following table shows the more common fluorescing minerals with their respective fluorescing colors, from Franklin and Sterling Hill, New Jersey.

Mineral:
Fluoresces:
Mineral:
Fluoresces:
Mineral:
Fluoresces:
Barite
white
Esperite
yellow
Margarosanite
pale violet
Calcite
red
Fluorite
Violet
Willemite
green
Clinohedrite
orange-yellow
Hardystonite
Violet-blue
Wollastonite
red

These minerals are sometimes found in association with each other and can make for wonderfully colorful fluorescent specimens. Esperite is a product of the metamorphism of zinc minerals, such as hemimorphite and/or smithsonite, that were caught up in the regional metamorphism that created the wonderful Franklin site. Esperite is found in significant quantities only at Franklin and Sterling Hill, New Jersey.

 

PHYSICAL CHARACTERISTICS:

  • Color is white or colorless.
  • Luster is vitreous or greasy to dull.
  • Transparency: Specimens are translucent to opaque.
  • Crystal System is monoclinic.
  • Crystal Habits include massive and granular specimens.
  • Cleavage is poor.
  • Hardness is 5.
  • Specific Gravity is approximately 4.3 - 4.4 (above average)
  • Streak is white.
  • Other Characteristics: Fluoresces a yellow color under short-wave UV light.
  • Associated Minerals include willemite, zincite, franklinite, larsenite, clinohedrite, calcite and hardystonite.
  • Notable Occurrences include its type locality at Franklin, New Jersey as well as Sterling Hill, Sussex County, New Jersey, USA and Bolivia.
  • Best Field Indicators are fluorescence, associations, locality and poor cleavage.




 

THE MINERAL EUCLASE

 


Euclase is not a well known gemstone, but is more well known by mineral collectors. It forms well formed crystals that occasionally have enough clarity to be cut as gems. The sapphire blue and blue green colors of euclase are the typical colors of the gemstones.

The crystals of euclase are commonly prismatic with slanted termination faces. Unlike other monoclinic minerals whose crystals will commonly look like higher symmetry crystals, euclase's crystals are distinctly monoclinic due to the slanted termination. Nice crystals of euclase are much sought after by collectors.

Euclase is found in granitic pegmatites with other gem minerals such as topaz and beryl. It is easily identified by its crystal form which can only be confused with barite or celestite but is the wrong environment for these sulfate minerals. Topaz has a completely different cleavage (basal) than euclase (prismatic). Transparent albite is softer. Euclase weathered out of source rock and transported down stream can end up being found in placer deposits with gold.
Euclase gets its name from its easy cleavage, euclase simply means easily cleaved. This is a problem for gem cutters who need to be careful of splitting an unfinished gem. It also detracts from it durability which limits its acceptance as a common gemstone. Another negative is its splotchy color distribution, but a skilled gem cutter can work a stone to its own advantage. Euclase is a real treasure in well formed crystals and in colorful gemstones.

 

PHYSICAL CHARACTERISTICS:

  • Color includes colorless, blue-green, blue, yellow, light green and rarely purple.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include stubby prismatic crystals with non-symmetrical slanted terminations.
  • Cleavage is perfect in one direction (prismatic), poor in two other directions.
  • Fracture is conchoidal.
  • Hardness is 7.5
  • Specific Gravity is 3.09 - 3.11 (slightly above average)
  • Streak is white.
  • Other Characteristics: Almost always striated lengthwise.
  • Associated Minerals include micas, quartz, topaz, beryl, gold, pericline and some feldspars.
  • Notable Occurrences include Ouro Preto and other areas within Minas Gerias, Brazil; Kenya; Tanzania; Ural Mountains, Russia; Germany and with emeralds in the famous mines of Columbia.
  • Best Field Indicators are crystal habit, good cleavage, striations, hardness and color.

 

 

 

 

THE MINERAL EUCRYPTITE

 

  • Chemistry: LiAlSiO4, Lithium Aluminum silicate.
  • Class: Silicates
  • Subclass: Nesosilicates
  • Group: Phenakite
  • Uses: Rarely cut as a gemstone, more common as mineral specimens.
  • Specimens

Eucryptite is one of the few silicate minerals that have a trigonal symmetry. This symmetry is far more common among carbonates than among silicates. Eucryptite shares the same symmetry with the emerald green silicate dioptase, phenakite and the fluorescent mineral willemite. Eucryptite belongs to the small Phenakite Group which includes only three minerals; eucryptite, phenakite and willemite. They all have the same basic structure, hence the same symmetry, but different metal ions.
  • Eucryptite's formula is LiAlSiO4.
  • Phenakite's formula is Be2SiO4.
  • Willemite's formula is Zn2SiO4.

Phenakite is the most well crystallized of the three in general, forming the best crystal shapes and the only one consistently cut as gemstones. Willemite is famous for fluorescing a bright green color under UV light and is found in mass at Franklin and Sterling Hill, New Jersey. Eucryptite is rarely cut as a gem and only some specimens fluoresce a pink color, but none the less it can be a interesting mineral for collectors.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually colorless or white.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System: trigonal; bar 3
  • Crystal Habits include granular grains and massive forms. Some crystals can be well formed with trigonal prisms with rhombohedral terminations. Eucryptite can also replace spodumene forming pseudomorphs.
  • Cleavage in poor in three directions.
  • Fracture is conchoidal.
  • Hardness is 6.5
  • Specific Gravity is approximately 2.67 (average for non-metallic minerals).
  • Streak is white.
  • Other Characteristics: Prism faces striated lengthwise, index of refraction is 1.55 and some specimens fluoresce pink under UV light.
  • Associated Minerals include quartz, micas, feldspars and spodumene.
  • Notable Occurrences include the type locality of Branchville, Fairfield County, Connecticut, USA as well as Harding Mine, Dixon, New Mexico and Parker Mountain, Stafford, New Hampshire, USA and Bikita, Zimbabwe
  • Best Field Indicators are crystal habit, striations, environment and hardness.

 

 

 

 

THE MINERAL EUDIALYTE

 

  • Chemistry: Na4(Ca, Ce, Fe, Mn)2ZrSi6O17(OH, Cl)2, Sodium Calcium Cerium Iron Manganese Zirconium Silicate Hydroxide Chloride
  • Class: Silicates
  • Subclass: Cyclosilicates
  • Uses: As mineral collection specimens and rarely cut as a gemstone.
  • Specimens

Eudialyte is a fairly rare cyclosilicate mineral. It is a popular mineral in collections however due to its attractive and distinctive colors. It unfortunately rarely forms good crystals and only occasionally forms any crystal faces at all. Crystals of eudialyte are usually embedded in the host rock, surrounded by other minerals and not showing any hint of a crystal form. The mineral's colors on the other hand are quite pleasant and give the collector an all-together attractive and rare mineral. It can show distinctive colors of a red-violet, pink, blue, yellow and an attractive brown. Much eudialyte on the market today comes from the Kola Peninsula, Russia and can add to one's collection of fine minerals from this wonderful site.

The site at Kola Peninsula is one of several sites around the world that have a strange assortment of igneous minerals and are referred to as Agpaitic Pegmatites. These sites are unusually rich in alkali metals especially sodium. They also tend to be rich in what are sometimes termed "difficult elements", elements that are large and/or have unusual charges. These elements do not fit well into ordinary minerals and are thus excluded from earlier crystallized minerals and must wait for their opportunity to crystallize later. Examples of difficult elements are zirconium, beryllium, strontium, cerium, niobium, thorium, barium, yttrium and other rare earth elements. These normally scarce elements become highly concentrated, relatively speaking, and form some unique and wonderful mineral species. Eudialyte is an example of an unusual mineral that comes from these mineralogically unique sites. Not only is it rich in sodium, but has zirconium, cerium and often traces of yttrium in its structure. Eudialyte is considered to be a potential source of zirconium in the future.

 

PHYSICAL CHARACTERISTICS:

  • Color varies from red-violet, pink, blue, yellow and a light brown.
  • Luster is vitreous.
  • Transparency: Crystals are translucent to transparent.
  • Crystal System is trigonal; bar 3 2/m.
  • Crystal Habit is typically embedded grains and distorted rhombohedral crystals.
  • Cleavage is poor in one direction (basal).
  • Fracture is uneven.
  • Hardness is 5 - 5.5
  • Specific Gravity is 2.9 (average)
  • Streak is white.
  • Other Characteristics: Crystals tend to be fractured and are somewhat brittle.
  • Associated Minerals include many rare minerals as well as nepheline, feldspars especially albite, and natrolite, quartz, calcite and aegirine.
  • Notable Occurrences include Mont Saint-Hilaire, Quebec, Canada; Kola Peninsula, Russia; Kangerdluarsuk and Julianehaab, Greenland; the Langesundfjord region of Norway; Madagascar and Magnet Cove, Arkansas, USA.

 

 

THE MINERAL EUDIDYMITE

 


Eudidymite forms a unique twin for which it is named. The twinning forms stellate figures with wedge shaped spokes. This habit is common for eudidymite and is quite distinctive. Eudidymite gets its name from the Greek words for "good" - eu and "twin" - didymus in allusion to its "good twin" habit.

It is interesting to note the difference between the naming of the minerals eudidymite and epididymite. Epididymite gets its name from the Greek words for "near" - epi and "twin" - didymus in allusion to its "near twin", eudidymite. Epididymite and eudidymite are not actually twins of course, but dimorphs! Dimorphic minerals are minerals that share the same chemistry, in this case NaBeSi3O7(OH); but they have different structures. Epididymite's structure is orthorhombic and eudidymite's structure is monoclinic in symmetry. The best known dimorphs are diamond and graphite, both of which are made of carbon, C, but have very different structures.

Eudidymite and epididymite are found in the unusual igneous intrusive rocks called agpaites. These rocks are similar to nepheline-syenites but are enriched in alkali metals and exotic elements and conversely low in aluminum and silica. Sodium is the chief alkali metal that is present in agpaites and so it is no surprise it is found in eudidymite. Beryllium is one of those exotic elements that is in unusual concentrations in agpaites and thus allows minerals like eudidymite to form. It is the collector that is rewarded by these unusual rare mineral producing rocks and agpaite deposits are always on the "locality radar" of mineral collectors. Places like Kola Peninsula, Russia; Mont Saint-Hilaire, Canada; Langesundfjord, Norway and Narssarssuk, Greenland are all top sites for these rare silicate minerals.

 

PHYSICAL CHARACTERISTICS:

  • Color is usually white or colorless, but can be pale pink, gray, yellow, blue or violet.
  • Luster is vitreous to silky or pearly.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m.
  • Crystal Habits include tabular crystals and aggregate spherulites. Twinning forms stellate figures with wedge shaped spokes.
  • Cleavage: is perfect in two directions.
  • Fracture is uneven.
  • Hardness is 6 - 7.
  • Specific Gravity is approximately 2.5 - 2.6 (average for translucent minerals).
  • Streak is white.
  • Associated Minerals include nepheline, aegirine, catapleiite, natrolite, fluorite, rhodochrosite, feldspars, micas and analcime.
  • Notable Occurrences include Kola Peninsula, Russia; Mont Saint-Hilaire, Quebec, Canada; Langesundfjord, Norway and Narssarssuk, Greenland.
  • Best Field Indicators are crystal habit, cleavage, associations, locality and hardness.

 

 

 

 

 

THE MINERAL EUXENITE

 

  • Chemical Formula: (Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Ti)2O6, Yttrium Calcium Erbium Lanthanum Cerium Uranium Thorium Niobium Tantalum Titanium Oxide.
  • Class: Oxides and Hydroxides
  • Uses: A minor ore of rare earth elements and uranium, sometimes cut as a gemstone and as mineral specimens.
  • Specimens

Euxenite, which is sometimes named euxenite-(Y) (the Y is for the yttrium), is a mineral that is sometimes called a "trash can mineral". Because it will accommodate a wide variety of elements in its crystal structure, generally the elements that other minerals do not seem to want, ie the "trash". For euxenite, these elements are in a group called the rare earths and are sometimes quite valuable, making euxenite a potentially profitable ore. Euxenite's name is from a Greek phrase meaning "hospitable", another reference to its . . . accommodating nature.

Euxenite is in a series with the mineral polycrase, another "trash can mineral". Polycrase is simply richer in titanium as opposed to the niobium rich euxenite. The other elements can be found in both minerals and the structure is basically the same.

Because of the rare earths metals in its structure, euxenite is one of several so called Rare Earth Oxides. Other rare earth oxides such as fergusonite, aeschynite and samarskite have very similar properties to euxenite and are often associated with each other, compounding the problem. Even the common oxide, rutile, is almost indistinguishable from these rare earth oxides without chemical tests when rutile is found massive.

Euxenite is found in rare earth rich, granite pegmatites, a slow cooling igneous intrusive rock. Euxenite is associated with quartz, feldspars, columbite, tantalite, monazite and other rare earth minerals. Euxenite is used as an ore for its rare earth metals and uranium. But it is its gemstone use that is what is odd about this mineral. Like samarskite, euxenite is sometimes cut into attractive gems and used as cabochons, although since the stones are slightly radioactive, their use as wearable gemstones should be quite ...well...risky!

Euxenite is an interesting and at times attractive mineral. Although most crystals are embedded and do not show good form, some crystals are exceptional and can demonstrate a high luster. Remember, this is a slightly 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 black with a tinge of yellow, brown or green.
  • Luster is greasy to submetallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include tabular to prismatic crystals with domal terminations and often embedded in the matrix of the host pegmatite; as well as granular and massive.
  • Cleavage is absent.
  • Fracture is conchoidal.
  • Hardness is 5.5 - 6.5
  • Specific Gravity is approximately 4.3 - 5.9 (heavy for non-metallic minerals). Extreme variation caused by variable composition of component metals.
  • Streak is yellow, brown or gray.
  • Other Characteristics: Slightly radioactive and crystals/specimens are often coated with a yellow limonite like earthy coating.
  • Associated Minerals include quartz, feldspars, molybdenite, chalcopyrite, fergusonite, monazite, columbite, tantalite, allanite, gadolinite, and zircon
  • Notable Occurrences include the Ural Mountains of Russia; Iveland, Aust-Agder, Norway; Sweden; Minas Gerais, Brazil; Ampangabe, Madagascar; Quadeville, and Madwaska, Ontario, Canada; sites in the White Tank Mountains and Kingman Quarry, Arizona; Encampment, Wyoming and in Colorado, USA.
  • Best Field Indicators are luster, fracture, color, radioactivity, associations, environment and specific gravity.
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