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Tanzanite
Scheelite:
Scheelite is calcium tungstate, an important ore of
tungsten. Crystals are, in general, rare, and face table
crystals rarer still. The ness is 41/L-5 on the Mohs
scale, with no pronounced cleavage. The w Is cut only
for collectors, and may occur in colorless, yellow,
brownish, or orange crystals. Good gem material comes
from Califor¬nia, Arizona and Mexico.
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Serpentine:
Few materials are as readily confused with jade as serpen¬tine
specially the variety called bowenite. Serpentine colors
are much like those of jade, in the green and yellowish
range. Mottled dark-green serpentine is called Verd
antique" and is used as a building stone. |
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Bowenite
is softer than jade and has a lower S.G. and refractive index.
hardness of serpentine is 21/2-4, that of bowenite 5-51/z.
Both materials are extensively used for carving and cabochons.
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Tanzanite |
| Tanzanite
There
is tremendous variety in the texture, color, and
appearance of serpentine minerals, and confusion
is commonplace. Detailed gemological tests usually
required to verify the authenticity of a jade
item, but the simplest preliminary test is simply
to scratch the item in question,Sphalerite: Sphalerite
is zinc sulfide, the world's principal ore of
is mined in enormous tonnages throughout the world,
but crystals Usually black or opaque red-orange.
Sometimes transparent masse - found, typically
red-orange in color, sometimes yellow or greenish
hardness is only 3'/z and the perfect cleavage
in six directions m, cutting and wearing difficult,
but the dispersion is nearly four time ¬of
diamond. Properly faceted gems are truly dazzling
and color Face table material comes from Spain,
Colorado, and Japan.
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Sphene:
Sometimes known as titanite, Sphene is seen often
enough jewelry to be classified as an almost commercial
stone. The color be green, brown, yellow, or some
combination of these three, are chrome-green colored
Sphene also exists, but is extremely rare. hardness
is 5-5'/z and toughness only fair; Sphene tends
to be brittle the dispersion is slightly higher
than that of diamond, so faceted gems are fiery
and brilliant.
The
usual cutting style is the round brilliant. (
, material comes from Brazil and Baja California.
Fine cut stones may for more than $100 per carat.
Thomsonite:
A complex silicate mineral, thomsonite is usually
found as Clue banded material in shades of brown,
green, yellow, pink, and white. The only noteworthy
locality is Harbor Bay, Lake Superior. The hardness
is 5-51/2, with good toughness. Thomsonite usually
forms as cavity fillings in volcanic rock. Weathering
of the rock releases the thomsonite which is tumbled
into rounded pebbles.
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Wulfenite:
A rare and beautiful gem, wulfenite is lead molybdate, an
,of molybdenum and lead. Its crystals, occurring in shades
of yellow, orange, and red, are highly prized by mineral
collectors. Cut gems have high dispersion and are spectacularly
colorful. Of equal value to gem have collectors are stones
displaying a rich orange or deep-red color. The mineral
is soft, only 3 on the Mohs scale, very brittle, and difficult
to cut.
Pale-yellow
crystals from Tsumeb, South West Africa have afforded gems
weighing more than ten carats. These resemble off-color
diamonds. Localities for gem material are limited: Arizona
and South West Africa.
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