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 spiderweb turquoise in almost any color,
robin’s egg blue or deep-blue azure in Europe.
In American 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.
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
