Chemistry of Turquoise
Here are some brief Chemical Turquoise Facts: - Turquoise
is a hydrated phosphate of aluminum and copper (copper aluminum
phosphate) or CuAl6((OH)2/PO4)4 CuAl6(PO4)4(OH)8 + 4H2O. In the
language of chemists and geologists, turquoise is known as. Turquoise
stones can contain impurities that form veins of sandstone, limonite,
psilomelane or jasper. At temperatures of 500 degrees, blue Turquoise
stones will become greener.
Color of Turquoise
Turquoise is a non-translucent stone whose most valuable specimens
are a spider web turquoise in almost any color, robin’s egg
blue or deep-blue azure in Europe. In American spider web or pattern
matrix bearing stones with great color are the most valuable, most
of which come from Arizona, Colorado, New Mexico, and Nevada. North
American specimens also contain impurities that form matrix streaks
within the stones. The veins are inclusions from nearby rock fragments
or oxides and form during the creation of Turquoise. As mentioned
above these veins can contain sandstones, limonite, malachite, chrysocolla
jaspers or psilomelane. The veins in some stones interlock in patterns
to form "spider-web" turquoise.
Crystal Habit of Turquoise
Nearly all Turquoise is cryptocrystalline. In fact, scientists
had thought Turquoise was amorphous (non-crystal forming) until
1911, when crystalline specimens were found in Virginia.
The Turquoise crystal system is Triclinic, which is the least
symmetrical of all crystal systems with all three axes of unequal
lengths and none intersecting at right angles. The common shape
for this system is the pinacoid.
Turquoise Facts on the Geological Environment
The common environment of Turquoise is arid or semiarid zones
such as those that occur in Iran or the Desert Southwest of the
United States. It is found in veins and nodules in weathered rhyolitic
igneous rock where it forms as a secondary mineral of the process
known as hydrothermal replacement depositing that occurs when chemicals
leach out of nearby rock by way of rain or a saturated water table.
Copper eroding from deposits leaches into cracks and combines with
phosphates and Turquoise’s other chemicals.
Turquoise Facts on Enhancements
Turquoise is a controversial stone because most of the stones
sold have received so many treatments that the final product is
completely different from its original form. Enhancements can include,
plastic, wax and oils that change color, durability and polish.
Turquoise Facts on Hardness
Turquoise has a hardness of 5.5 to 6.5 on Mohs Scale. The process
by which Turquoise forms creates a porous stone. The harder, less
porous stones polish better than the pale softer, chalky stones
but these can have waxes or oils pressed into them to help their
polish.
Imitators of Turquoise
Because of the rarity of fine specimens of Turquoise, jewelry
makers have been creating imitations of it for centuries. The Egyptians
used a glazed quartz paste as a substitute for the Turquoise for
their jewelry requirements. The most common modern imitators of
Turquoise are Howlite, Magnesite, Turquenite, dyed chalcedony, glasses,
ceramics, and plastics. The minerals most often confused with Turquoise
include Amazonite, Prosopite, Lazulite, Hemamorphite, Chrysocolla,
Odontolite, Serpentine, Smithsonite, Faustite, and Variscite. Bone
Turquoise or Vivianite (a hydrous ferrous phosphate) can leach into
fossils and turn them a blue that is close to Turquoise in color.
Reconstituted Turquoise-The process of reconstituting Turquoise
consists of pulverizing pieces of turquoise that are then stabilized
and hardened with resins to achieve a natural Turquoise appearance.
Resin-reconstituted Turquoise usually has an odor that allows for
detection.
Lab-Grown Synthetic Turquoise: Also known as Neo-turquoise,
Hamburger Turquoise or Neolite. Lab-grown Turquoise does not have
the veins of impurities found in most American Turquoise. The refractive
index of natural Turquoise is usually slightly higher than that
of lab-grown stones. Genuine specimens also have homogenous blue
matrices that contain irregular white particles.
Turquoise Care Facts
The most common dangers to Turquoise are scratches, sharp blows,
hot water, and household chemicals. Because it is a hydrous stone,
water or light can change the color of Turquoise stones and its
relative softness can make it vulnerable to scratches. The pores
of the stone will easily absorb body oils or other oils causing
the stone to yellow over time. Do not use an ultrasonic cleaner
on Turquoise and avoid chlorine.
Chem: CuAl6(PO4)4(OH)8 * 5H2O Hydrous copper aluminum phosphate
Color: sky blue, bluish-green, pale green, dark "forest"
green, dark "sky" blue
Refrac. Index: 1.61 - 1.65
Birefraction: 0.04
Hardness: 5 - 6
Spec. Grav.: 2.60 - 2.80
Specific Gravity: 2.6 to 2.8
Cleavage: none
Fracture: conchoidal, uneven
Transparency: opaque
Chemical Composition: CuAl6((OH)2/PO4)4 CuAl6(PO4)4(OH)8 + 4H2O
Luster: waxy, vitreous in macro-crystals
Color of streak: white, usually with brown or black spots, or white
with greenish tint
Class: phosphates
Crystal System: triclinic; bar 1; rarely seen in crystalline form,
most stones are cryptocrystalline
Best Field Indicators: crystal habit, hardness, luster, color and
associations
See Also: TurquoiseFacts.com
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