Dioptase
| Dioptase | |
|---|---|
Dioptase from Altyn Tübe, Kazakhstan, the type locality
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| General | |
| Category | Cyclosilicates |
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Formula (repeating unit) |
CuSiO3·H2O |
| Strunz classification | 9.CJ.30 |
| Crystal system | Trigonal |
| Crystal class | Rhombohedral (3) H-M Symbol: (3) |
| Space group | R3 |
| Unit cell | a = 14.566, c = 7.778 [Å]; Z = 18 |
| Identification | |
| Color | Dark blue green, emerald green |
| Crystal habit | Six sided prisms terminated by rhombohedrons to massive |
| Cleavage | Perfect in three directions |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5 |
| Luster | Vitreous |
| Streak | Green |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.28–3.35 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.652 - 1.658 nε = 1.704 - 1.710 |
| Birefringence | δ = 0.052 |
| References | |
Dioptase is an intense emerald-green to bluish-green copper cyclosilicate mineral. It is transparent to translucent. Its luster is vitreous to sub-adamantine. Its formula is CuSiO3·H2O (also reported as CuSiO2(OH)2). It has a hardness of 5, the same as tooth enamel. Its specific gravity is 3.28–3.35, and it has two perfect and one very good cleavage directions. Additionally, dioptase is very fragile and specimens must be handled with great care. It is a trigonal mineral, forming 6-sided crystals that are terminated by rhombohedra.
Dioptase was used to highlight the edges of the eyes on the three Pre-Pottery Neolithic B lime plaster statues discovered at 'Ain Ghazal known as Micah, Heifa and Noah. These sculptures date back to about 7200 BC.
Late in the 18th century, copper miners at the Altyn-Tyube (Altyn-Tube) mine, Karagandy Province, Kazakhstan thought they found the emerald deposit of their dreams. They found fantastic cavities in quartz veins in a limestone, filled with thousands of lustrous emerald-green transparent crystals. The crystals were dispatched to Moscow, Russia for analysis. However the mineral's inferior hardness of 5 compared with emerald's greater hardness of 8 easily distinguished it. Later Fr. René Just Haüy (the famed French mineralogist) in 1797 determined that the enigmatic Altyn-Tyube mineral was new to science and named it dioptase (Greek, dia, "through" and optos, "visible"), alluding to the mineral's two cleavage directions that are visible inside unbroken crystals.
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