THE MINERAL TURQUOISE

Chemistry: CuAl6(PO4)4(OH)8*5(H2O), Hydrated Copper Aluminum Phosphate
Class: Phosphates
Uses: as an ornamental stone for carving and jewelry.
Specimens

Turquoise is a valuable mineral and is possibly the most valuable, non-transparent mineral in the jewelry trade. It has been mined for eons since at least 6000 BC. by early Egyptians. Its history also includes beautiful ornamental creations by Native Americans and Persians. Its popularity is still quite strong today. Although crystals of any size are rare, some small crystals have been found in Virginia and elsewhere. Most specimens are cryptocrystalline, meaning that the crystals could only be seen by a microscope. The finest turquoise comes from Iran but is challenged by some southwestern United States specimens. Turquoise is often imitated by "fakes", such as the mineral chrysocolla, and poorer turquoise specimens are often dyed or color stabilized with coatings of various resins. The name comes from a french word which means stone of Turkey, from where Persian material passed on its way to Europe.

PHYSICAL CHARACTERISTICS:

Color is of course, turquoise, but this color actually varies from greenish blue to sky blue shades.
Luster is dull to waxy, vitreous in macro-crystals.
Transparency specimens are opaque.
Crystal System is triclinic; bar 1
Crystal Habits include crystals rarely large enough to see, usually massive, cryptocrystalline forms as nodules and veinlets.
Cleavage is perfect in two direction, but is not often seen.
Fracture is conchoidal and smooth.
Hardness is 5 - 6
Specific Gravity is approximately 2.6 - 2.8 (average)
Streak is white with a greenish tint.
Associated Minerals are pyrite. limonite. quartz and clays.
Other Characteristics: color can change with exposure to skin oils.
Notable Occurances include Arizona and New Mexico, USA; Australia; Iran; Afghanistan and other locallities in the Middle East.
Best Field Indicators are crystal habit, hardness, luster, color and associations.