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GemBits - Turquoise


#1

Prized for its sky-blue color, turquoise has been used in amulets
and jewelry since antiquity. The oldest known piece of jewelry is a
turquoise and gold bracelet found in the tomb of Zer, an Egyptian
queen who lived 7,500 years ago.

Turquoise is an anglicized version of turkois, which is French for
"Turkey stone." Originally mined in Persia (now Iran), turquoise
arrived in Europe via Turkey, hence the name. Persian turquoise is
noted for the purity of its blue color and experts regard it as the
finest of all turquoise. Most turquoise today comes from China,
Mexico and the United States; it’s no longer mined in Iran.

Depending upon its origin, turquoise may vary in color from pale
blue to bright green. Although pure sky blue is regarded as best by
many people, there is no ideal color. Each hue has its devotees.

Turquoise is found close to the surface in arid climates. Phosphate
and aluminum combine to form turquoise when surface waters seep into
underlying rocks. The blue comes from small amounts of copper, while
iron impurities yield a greenish color. Although sometimes found in
veins, turquoise most often occurs as nuggets.

The rock in which turquoise is formed is called a matrix. Turquoise
with parts of the rock still embedded in it is called matrix
turquoise. Nuggets may also contain small bits (inclusions) of
pyrite or other minerals. Iron oxide forms a webbed pattern of fine
lines, leading to the name “spiderweb” turquoise. Veining or a
mottled appearance in the stone is from the uneven distribution of
copper.

Natural turquoise is turquoise which has had nothing done to it that
changes or preserves the color, hardens or protects the surface or
makes it easier to work with. It’s usually just polished and placed
in a setting.

Because it is porous, natural turquoise is absorbent. Perfumes,
cosmetics, and perspiration can cause it to change color or become
dull. Excessive heat will destroy turquoise. It’s also a very soft
stone that requires care in wearing.

Turquoise is frequently treated in several ways, some of which are
nearly undetectable, even by experts. Treating turquoise often
preserves the color and protects the stone. It also salvages
otherwise unusable stones. Artificial, imitation and synthetic
turquoise are also on the market. As with treated turquoise, buying
these is only a problem if you think you’re buying natural stones.

The most common treatments are stabilization and enhancement. Most
stabilized turquoise has been impregnated with clear plastic.
Stabilized turquoise is no longer porous or subject to color
changes. It also allows holes to be drilled in nuggets or beads for
stringing. If a dye is added to the plastic, then the turquoise is
enhanced. Both stabilization and enhancement are permanent, unless
wax was used rather than plastic.

Thin pieces of turquoise may be backed with epoxy or artificial
matrix to add thickness or strength. Done well, the backing is
impossible to detect once the stone is set; however, it may dissolve
if cleaned in certain solvents.

Other, less-desirable treatments include dipping the stone in oil to
temporarily improve the color, using black shoe polish to create
"matrix" or “spiderwebbing” or using epoxy to fill holes or create
"pyrite" inclusions. Dyed howlite may be sold as "turquosite."
Gilson turquoise is a high-quality synthetic.

There are few nondestructive ways to test turquoise. Heat and
chemicals will destroy or damage both natural and treated turquoise.
Your best defense is to buy from reputable dealers and ask lots of
questions.

Ancient people wore turquoise to protect them from a multitude of
misfortunes, including disease, poison and snakes. It was especially
used to protect horseback riders from falls. Many believed that
turquoise had the power to attract love, wealth and beauty to those
who wore it.

****Sandra I. Smith, Writer ****