Jasper
Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. Jasper breaks with a smooth surface and is used for ornamentation or as a gemstone. It can be highly polished and is used for items such as vases, seals, and snuff boxes. The density of jasper is typically 2.5 to 2.9 g/cm3. Jaspillite is a banded-iron-formation rock that often has distinctive bands of jasper.
| Jasper | |
|---|---|
Jasper outcrop, Bucegi Mountains, Romania | |
| General | |
| Category | Mineral |
| Formula (repeating unit) | SiO2 (with varying impurities) |
| Crystal system | Hexagonal |
| Crystal class | Quartz (Chalcedony) |
| Identification | |
| Colour | Most commonly red, but may be yellow, brown, green or (rarely) blue |
| Cleavage | Indiscernible |
| Mohs scale hardness | 6.5–7 |
| Luster | Vitreous |
| Diaphaneity | Opaque |
| Specific gravity | 2.5–2.9 |
| Refractive index | 1.54–2.65 |
| Birefringence | 0.009 |
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