Turquoise
Turquoise means 'Turkish stone' because the trade route of this stone brought it to Europe used to come via Turkey. It is prized for its intense colour, which varies from sky-blue to green, depending on the quantities of iron and copper within it. Turquoise is commonly found in micro crystalline, massive from usually as encrustations, in veins or as nodules. It is opaque to semi translucent, light and very fragile with conchoidal fracture. Pure blue colour turquoise is rare. It has waxy or mat luster. The populer sky-blue colour changes at 2500oC into a dull green. It is very porous, leading to fading and cracking, so it may be impregnated with wax or resin to maintain its appearance. Sky-blue turquoise from Iran is generally regarded as the most desirable, but in Tibet a greener variety is preferred.
DEPOSITS
The best qualities of turquoise are found in Northeast Iran near Nishapur. Additional deposits are found in Afghanistan, Argentina, Australia, Brazil, China, Israel, Mexico, Tanzania and the United States.
PROPERTISE
| Species | TURQUOISE |
|---|---|
| Variety | Turquoise |
| ChemComp | Cu Al6 (PO4)4 (OH)8 5H2O with some alumina replaced by ferric Oxide. (Hydrous Phosphate of aluminium and copper with some iron) |
| Crystal System | Triclinic |
| Color | Ranges from blue to green to yellow green |
| Cause of color | Green-Copper and Iron. Blue - Copper. |
| Hardness | 5.5 to 6 |
| Specific Gravity | 2.60 to 2.85 |
| Pleochroism | Nil |
| R.I. Range | 1.610 - 1.650 |
| Optic Sign | B+ve |
| Birefringence | 0.04 |
INCLUSION
Inclusion Found in Turquoise is Pyrite, Quartz, Limonite
SIMMULANT
Variscite, dyed jasper, howelite, plastic, stained chalcedony, reconstructed and synthetic turquyoise, odontolite, smithsonite, chrysocolla.
