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Tanzanite
1967 the only variety of the mineral zoisite used for
gems was a colored, massive material known as thulite.
In 1967 transparent of violet-blue zoisite were found
in Tanga Province, Tanzania, and later in various deposits
in the Umba valley.
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The
crystals occur in various colors, including brown, pink,
yellow, and green; many crystals are strongly trichroic.
Careful heating about 700° F, however, turns most
of these crystals a uniform, deep violet-blue color.
Exquisite gems have been cut from this material, to
which Tiffany & Co. |
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gave
the trade name tanzanite. Initially a large -quantity of material
was available, and prices of even large stones varied up to
a few tens of dollars per carat. By 1975 the retail price
of large w weighing more than ten carats, could be measured
in hundreds of dollars per carat. Tanzanite offers a striking
testimony to the rapid and sizable appreciation possible in
certain gems.
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Tanzanite |
| Tanzanite
The
hardness of tanzanite on the Mohs scale is only
6, so the gem is a choice for a ringstone. In
addition there is one direction of perfect -.age
that makes wear in a ring inadvisable. The best
tanzanite's however, resemble fine blue sapphires,
and it is easy to see why they a become so popular.
Tanzanite is known only from Tanzania, and decreasing
production at the mines has made fine gems scarce.
Stones under two carats are available in fair
quantity, but larger stones that have no internal
flaws or inclusions are rare and costly.Amblygonite:
A rare phosphate mineral, generally colored yellow;
also brown, blue, green, and pink, sometimes colorless.
Hardness 6, concoidal fracture, and one good cleavage
direction. Localities include Brazil, California,
South Dakota, Maine, Spain, and Norway Cut gem
my resemble spodumene. Stones over 20 carats available.
. 
Andalusite:
Available in sufficient quantity to be popularized
on a limited scale, and may be seen in jewelry.
Most frequently cut in stones of one-two carats,
larger gems are rare. Named after Andalusia, Spain,
where first found; occurs sparingly in the gem
gravels of Sri Lanka but w, material is from Brazil.
Andalusite is very dichroic, the colors brownish-green
and reddish-brown; rarely seen are brown, pink,
sand violets tones. Hardness is 7'/z, cleavage
distinct, but the material is : wears well. Stones
are generally cut so that two of the , colors
are both visible at the same time, usually green
in the -,: brown at the ends. Cut Andalusite may
resemble tourmaline. Material sometimes contains
a black, cross-like core and is and is known chiastolite.
Localities for chiastolite include Maine, Massachusetts
and the U.S.S.R. |
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Apatite
: This would be a fine gem it not so soft, only 5 on the
Mohs -w color range includes yellow, violet, blue, green,
brown, and apatite is calcium phosphate, with no distinct
cleavage and uneven fracture. Faceted gems are relatively
easy to cut and take a high sometimes fibrous inclusions
will produce a cat's-eye effect.
Gem
material comes from Mexico (yellow), Sri Lanka (blue), Norway
(blue green), Canada (green, brown), India (green), Germany
(violet), and Maine (violet). Apatite has been synthesized
for use in lasers, but cut synthetics are not sold commercially.
Apatite is the material of which bones and teeth are made.
Organi¬cally created crystals tend to be extremely small,
whereas mineral crystals may reach a length of several feet!
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