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.
Turquoise is a non-translucent stone whose most valuable specimens
are a robins egg blue or deep-blue azure in Europe, most of these
fine specimens come from Iran and indicate the presence of copper within
the stone. In america spiderweb 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.
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
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 Turquoises
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 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.
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.
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
Hardness: 5 - 6
Spec. Grav.: 2.60 - 2.80
Specific Gravity: 2.6 to 2.8
Fracture: conchoidal, uneven
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
Crystal System: triclinic; bar 1; rarely seen in crystalline form, most
stones are cryptocrystalline
Best Field Indicators: crystal habit, hardness, luster, color and associations
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