The Mineral ZUENERITE
Zeunerite is a rare uranyl arsenate that is similar to the more well known uranyl phosphate mineral
torbernite. The two minerals are almost identical and share many similar properties. The association of zeunerite with other arsenic minerals is a key in distinguishing the two. Zeunerite in named for G. A Zeuner, a German physicist. Its pseudocubic crystals can be quite attractive.
The structure of zeunerite is composed of arsenate tetrahedrons linked to uranium-oxygen groups (called uranyl ions groups) that form distorted octahedrons. The arsenates and uranium groups form sheets that are weakly held together by water molecules. This structure produces the tabular habit, the one perfect direction of cleavage and the relative softness. It is an analogous structure to that of the
phyllosilicates. Zeunerite's structure produces a rather exclusive
symmetry,
bar 4. Only a few minerals share this symmetry.
Zeunerite can lose water and convert to a different mineral called
meta-zeunerite which belongs to the
meta-autunite/meta-torbernite group of minerals. The change to meta-zeunerite will often produce a pseudomorph. A pseudomorph is generally an atom by atom replacement of one mineral's chemistry to form another mineral. The process leaves the crystal shape of the lost mineral intact. The word pseudomorph means false shape. In this case, the conversion is not so dramatic since it involves only the loss of a few water molecules and therefore a good pseudomorph is likely. The conversion is irreversible and ongoing and all collection specimens of a certain age are partially to totally converted. Fine zeunerite specimens should be stored in a closed container to avoid water loss. Remember, this is a
radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should be limited!
PHYSICAL CHARACTERISTICS:
- Color varies from the typical emerald green to yellow.
- Luster is vitreous, pearly on cleavage surfaces.
- Transparency: Crystals can be transparent to translucent.
- Crystal System is tetragonal; bar 4
- Crystal Habits include tabular square crystals dominated by two pinacoid faces. Bipyramidal crystals are also seen. Crystals can look cubic (pseudocubic) too. Also as crusts, micaceous, foliated and earthy.
- Cleavage is perfect in one direction (basal).
- Fracture is uneven.
- Hardness is 2 - 2.5
- Specific Gravity is approximately 3.2 - 3.4 (slightly above average for translucent minerals)
- Streak is a pale green.
- Other Characteristics: Radioactive, non-fluorescent and cleavage sheets are not bendable but are in fact brittle.
- Associated Minerals are barite, fluorite, olivenite, brochantite, scorodite, heinrichite, mixite, walpurgite, uraninite and other uranium minerals.
- Notable Occurences include Grandview Mine, Arizona, USA; Weisser Hirsch Mine, Schneeberg, Saxony, Germany; Wheal Edward Mine, Cornwall, England and other localities with uranium arsenic minerals.
- Best Field Indicators are color, crystal habit, non-fluorescence, radioactivity, associations especially with arsenic minerals and brittle cleavage sheets.
The Mineral NATIVE ZINC
Native zinc is a rare mineral. Native zinc has been found in several locations but is never found in any abundance. It would be wrong to consider it an ore of zinc. First of all, an ore should be less valuable than its constituent metal. And since zinc is so rare in its native form, this is not true. Secondly, an ore needs to be common enough and exploitable enough to be profitable enough to mine. In other words, economical! As already stated, native zinc is a rare mineral and in addition, it does not group itself in any siginificant concentrations. Actual ores of zinc include
sphalerite, smithsonite, hemimorphite, franklinite, willemite, hydrozincite and
zincite. Zinc is used in a variety of special alloys that have unique industrial properties from great strength to unusual plasticity.
Native zinc's type locality is somewhat in doubt as different localities are sometimes mentioned. The Mina Dulcinea de Llampos, Copiapo, Chile locality seems to be the current type locality of concensus, however a case has been made for the first specimens of native zinc actually coming from New Brunswick, Victoria, Australia in 1855. Native zinc is found as indistinct grains in igneous rocks with originations from a reducing environment.
As an important industrial metal, zinc has been used for eons, even if its users did not know what it was. It was used to make the zinc/copper alloy brass in prehistoric times. A figure in the Bible, Tubal-cain, was mentioned as an instructor in brass and iron. The Bible says he was 7 genenerations from Adam. Prehistoric brass has been found in Romanian ruins. Romans made great use of brass and found it to be ornamental as well as useful. It is doubtful that the zinc metal was actually seen by its early users as it boils well below copper's melting point and thus can not be melted into the copper. More likely a technique was used that roasted the zinc ores with the copper and the resultant zinc fumes absorbed into the melting copper.
There are a few naturally occurring zinc alloys that are classified in the
Elements Class with native zinc. Naturally occurring
brass, Cu3Zn2, is one of them. It is being given consideration as a mineral, but is not yet officially recognized. Other zinc alloy minerals include
danbaite, CuZn2 and
zhanghengite, (Cu, Zn, Fe, Al, Cr). PHYSICAL CHARACTERISTICS:
- Color is white to bright blue gray.
- Luster is metallic.
- Transparency: Specimens are opaque.
- Crystal System is hexagonal; 6/m 2/m 2/m.
- Crystal Habits include volcanic exhalations, granular (often microscopic) and lab grown specimens.
- Cleavage is perfect in one direction (basal).
- Hardness is 2.
- Specific Gravity is 6.9 - 7.2 (heavy even for a metallic mineral).
- Streak: Light gray.
- Other Characteristics: Brittle at room temperatures (not malleable or ductile unless heated to 100 degrees C).
- Associated Minerals include native gold, native copper, native aluminum and other rare native metals.
- Notable Occurrences include the type locality of Mina Dulcinea de Llampos, Copiapo, Chile and Elsa Mine, Keno Hill-Galena Hill area of the Yukon Territory, Canada as well as New Brunswick, Victoria and Forest Range Gold Mine, Australia; Tyrol, Austria; Amur, Yakutia; Chirynaisky Massif, Koryak Mts., Kamchatka Peninsula and Billeekh Intrusion, Siberia, Russia.
- Best Field Indicators are color, brittleness, hardness, locality and density.
The Mineral ZINCITE
Zincite is a one locality mineral. Well actually that is not true. It is found at several localities around the world; and is rare and inconspicuous at all but one general site. That site is the famous zinc and manganese mines of the Sterling Hill and Franklin, New Jersey, USA area. Many rare minerals are found there and zincite although rare everywhere else, is far from rare there. So abundant was zincite that it was quickly exploited and became an important ore of zinc.
The structure of zincite consists of tetrahedrons of ZnO
4. The tetrahedrons in zincite all are oriented in one direction and produce the hexagonal (six fold rotational) symmetry. The major axis is symmetrically polar and results in a hemimorphic crystal structure. In other words, there is no symmetry element, like a mirror or two fold rotational axis, perpendicular to the major axis and thus crystal faces on top of the crystal are not repeated on the bottom of the crystal. Hemimorphic crystals have different looking tops from their bottoms, as if they never completed the opposite, symmetrical, side; therefore the term hemimorphic or
half shape. Other minerals besides zincite that have a hemimorphic character are the
tourmalines, hemimorphite (what's the first clue?),
greenockite and
wurtzite; among others.
PHYSICAL CHARACTERISTICS:
- Color is orange-yellow to deep red or brown.
- Luster is adamantine.
- Transparency crystals are commonly translucent more rarely transparent.
- Crystal System is hexagonal; 6 m m
- Crystal Habits include rarely well shaped, over all, hemimorphic pyramidal crystals sometimes with an hexagonal prism terminated by the basal face of a pedion on one side and the sharp point of the pyramid on the other. Usually found as rounded granular crystals; also massive in veins and lamellar.
- Cleavage is good in three directions (prismatic).
- Fracture is conchoidal.
- Hardness is 4
- Specific Gravity is 5.4 - 5.7 (slightly heavy even for metallic minerals)
- Streak is orange-yellow.
- Other Characteristics: There is a basal parting.
- Associated Minerals include calcite, rhodonite, willemite, franklinite, tephorite, pyroxmangite and other rare Sterling Hill and Franklin, New Jersey minerals.
- Notable Occurrences include the Sterling Hill and Franklin, New Jersey, USA locations where it is found in abundance. Some occurrences from where zincite is found but in much scarcer quantities include Tuscany, Italy; Tsumeb, Namibia; the Dick Weber Mine, Colorado, USA; Poland, Spain and Tasmania, Australia.
- Best Field Indicators are luster, color, occurrence, associations, cleavage, parting and streak.
THE MINERAL ZINKENITE
- Chemistry: Pb9Sb22S42, Lead Antimony Sulfide
- Class: Sulfides
- Subclass: Sulfosalts
- Uses: Mineral specimens and as a very minor ore of lead.
- Specimens
Zinkenite is one of a few sulfide minerals that form fine acicular crystals that appear as hair-like fibers. The fibrous aggregates may be so thick as to cover a specimen with a mat of hair-like fibers or it may be sparsely dessiminated between other minerals and may be confused with stray hairs or dark lint.
Jamesonite, boulangerite and
millerite are other sulfides that form similar acicular crystals. These sulfides as well as zinkenite have been called
"feather ores" because of this unusual habit. Zinkenite is a sulfosalt, a segment of sulfides where the antimony acts more like a metal than a non-metal and occupies a position where it is bonded to sulfurs. A variety of zinkenite from Tasmania contains a small amount of silver.
PHYSICAL CHARACTERISTICS:
- Color is steel gray to gray.
- Luster is metallic.
- Transparency: Crystals are opaque.
- Crystal System: Hexagonal.
- Crystal Habits include dense or sparse felted masses of acicular crystals. Also in fibrous and compact plumose (feathery) masses. Larger crystals show hexagonal prismatic and pyramidal forms.
- Hardness is 3 - 3.5
- Specific Gravity is 5.3 - 5.35 (somewhat heavier than average for metallic minerals)
- Streak is steel gray.
- Other Characteristics: Crystals are brittle.
- Associated Minerals include quartz, calcite, arsenopyrite, jamesonite, boulangerite and other sulfosalts.
- Notable Occurrences include Wolfsberg, Harz, Germany; Dundas, Tasmania, Australia; Silverton, Colorado and Nevada, USA; Bolivia and in British Columbia, Canada.
- Best Field Indicators are crystal habit, associations, color and luster.
THE MINERAL ZINNWALDITE
- Chemistry: K Li Fe Al (AlSi3 ) O10 (OH, F)2, Potassium lithium iron aluminum silicate hydroxide fluoride.
- Class: Silicates
- Subclass: Phyllosilicates
- Group: Micas
- Uses: mineral specimens and limited use as electrical and heat insulator for industrial purposes.
- Specimens
Zinnwaldite is a very rare member of the mica group and is not well known even by mineral collectors. Zinnwaldite is darker colored than typical muscovite but lighter than phlogopite or biotite The dark color and density in the three iron containing micas increase with an increase in the iron and magnesium content. Zinnwaldite is difficult to distinguish from the other micas at least by ordinary methods and lacallity and enviroment are keys to identification. It is limited to special granites and their pegmatites. Zinnwaldite, like other micas, has a layered structure of lithium iron aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Zinnwaldite is rarely available to collectors but some nice specimens with apatite are now on the market showing nice tabular crystals.
PHYSICAL CHARACTERISTICS:
- Color is pale brown to gray and even green.
- Luster is vitreous to pearly.
- Transparency crystals are transparent to translucent.
- Crystal System is monoclinic; 2/m
- Crystal Habits include mostly tabular crystals with a prominant pinacoid termination. Zinnwaldite's four prism faces and two pinacoid faces form pseudo-hexagonal crystal "books". The sides of the crystal often tend to tapper 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 - 3.2+ (average to slightly above average)
- Streak is white.
- Associated Minerals are quartz, apatite, feldspars and tin minerals.
- 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 Cornwall, England; Germany and San Diego, California.
- Best Field Indicators are crystal habit, color, cleavage, elastic sheets, enviroments and associations.
THE MINERAL ZIPPEITE
- Chemistry: K4(UO2)6(SO4)3OH10-4H2O , Hydrated Potassium Uranyl Sulfate Hydroxide
- Class: Sulfates
- Uses: a minor ore of uranium and mineral specimens
- Specimens
Zippeite is a rare mineral but is sought after by collectors who seek uranium bearing minerals as well as minerals that have exotic names. Zippeite fluoresces under ultraviolet light. The mineral is inconsistent however in the color that is produced. Zippeite is formed as a secondary mineral and as an efflorescent crust in uranium mines. Efflorescent means it forms on the surface of a rock by the evaporation of water when in contact with the dry air of the mine. Thus, some zippeite specimens are the result of human intervention (albeit unintentional) and some minerologists do not consider these to be pure mineral specimens. Remember, this is a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should be limited.
PHYSICAL CHARACTERISTICS:
- Colors are various shades of golden-yellow to orange-yellow and sometimes brown.
- Luster is dull
- Transparency crystals can be transparent to translucent.
- Crystal System is orthorhombic.
- Crystal Habits are usually limited to encrustations and compact masses.
- Cleavage not seen.
- Hardness is approximately 2.
- Specific Gravity is approximately 3.7+ (above average for non-metallic minerals)
- Streak is a pale yellow.
- Associated Minerals are autunite, torbernite, uraninite and other uranium minerals.
- Other Characteristics: radioactive and fluoresces different colors from different specimens.
- Notable Occurances include Cornwall, England; Utah and Colorado, USA and the Bohemian region of Europe.
- Best Field Indicators are color, crystal habit, fluorescence, softness, luster and radioactivity.
THE MINERAL ZIRCON
Zircons reputation has suffered of late due to the introduction of a diamond simulant. So for the record, zircon is
NOT the same material as the artificial gem material
Cubic Zirconia (or CZ). However with that in mind, zircon has been used as a diamond simulant both for innocent and nefarious reasons. Zircon resembles diamond in luster and fire and colorless zircons have been mistaken for diamonds by experienced jewelers. Zircon can make a very attractive and affordable gemstone. It is found in browns and greens but can be heat treated to beautiful blue and golden colors. Colorless material is produced in this way as well. Zircon is the December
Birthstone.
As a mineral specimen, zircon is uncommon in most rock shops because attractive specimens are rare. However, fine specimens of well shaped zircons are available and are in demand. The typical simple crystal of zircon is a tetragonal prism terminated with four sided pyramids at each end. The prism may be lacking and the crystal can look octahedral. More complex crystals have faces of a less steeply inclined prism that taper the terminations. Also a secondary prism may truncate the primary prism by cutting off its edges and producing an octagonal cross-section through the crystal. There is even an eight sided pyramid (actually a ditetragonal dipyramid) that may modify the four sided pyramids. As you can see, zircon crystals can go from a very simple crystal to a rather complexly faceted form.
PHYSICAL CHARACTERISTICS:
- Color is brown, red, yellow, green, blue, black, and colorless.
- Luster is adamantine.
- Transparency crystals are transparent to translucent.
- Crystal System tetragonal; 4/m 2/m 2/m
- Crystal Habits: dipyramidal and prismatic as discussed above.
- Cleavage indistinct in two directions, prismatic.
- Fracture is uneven
- Hardness is 7.5
- Specific Gravity is 4.6-4.7
- Streak white
- Associated Minerals albite, biotite, garnets, xenotime and monazite.
- Other Characteristics: is sometimes fluorescent and darker crystals may be radioactive due to impurities of rare earth elements. Also index of refraction is 1.92 - 2.01
- Notable Occurances Seiland, Norway; Pakistan; Russia; Bancroft and Sudbury, Ontario, Canada and New Jersey and Colorado, USA.
- Best Field Indicators are crystal habit, hardness, luster and density.
THE MINERAL ZOISITE
Zoisite, like all epidote minerals, is a structurally complex mineral having both single silicate tetrahedrons, SiO4, and double silicate tetrahedrons, Si2O7. The formula of zoisite could be expressed in a such a way so as to reflect this organization; Ca2AlOAl2(SiO4)(Si2O7)(OH).
Zoisite has been known for nearly two centuries as as a sometimes ornamental stone of limited distribution. Only in 1967 was the blue gemstone variety found in Tanzania. The variety was named
Tanzanite and was a surprise to minerologists and gemologists alike in that it had come from a very ungemstone-like mineral. The blue-lavender color of tanzanite is unique and sets it apart from the other gemstones.
Besides tanzanite, zoisite has produced other attractive specimens that are of interest to collectors. A pink variety called
thulite is usually massive and used for beads and cabochons. A brilliant green variety is associated with medium grade
rubies and is quite popular as an ornamental stone. The red rubies are often distorted and irregularly spread throughout the sea of massive green zoisite. It is one of the most colorful of ornamental stones and competes well with the popular pink
tourmaline and lavender
lepidolite of California.
PHYSICAL CHARACTERISTICS:
- Color is variable but well known as green, blue to violet and pink to reddish in color, Also grey, white or brown.
- Luster is vitreous.
- Transparency crystals are transparent to translucent.
- Crystal System orthorhombic; 2/m 2/m 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 usually poorly developed. Also massive or granular.
- Cleavage good in one direction lengthwise.
- Fracture is uneven to conchoidal.
- Hardness is 6 - 7
- Specific Gravity is approximately 3.3
- Streak is white.
- Other Characteristics: striated crystals common, lengthwise. Also strongly pleochroic with an index of refraction of 1.68 - 1.72.
- Associated Minerals include calcite, biotite, hornblende, quartz, corundum, andradite garnets and other metamorphic minerals.
- Notable Occurances include Tanga, Tanzania; Ducktown, Tennessee, USA; Switzerland, India and Austria.
- Best Field Indicators only one direction of cleavage, associations, color, pleochroism and hardness.
