Jasper
| Jasper | |
|---|---|
 Jasper outcrop, Bucegi Mountains, Romania | |
| General | |
| Category | Aggregate rock (impure chalcedony variety) |
| Formula | SiO2 (with varying impurities) |
| Crystal system | Hexagonal |
| Identification | |
| Colour | Most commonly red, but may be yellow, brown, green or (rarely) blue |
| Crystal habit | Massive |
| Cleavage | none |
| Fracture | Conchoidal |
| 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 |
Jasper is an opaque type of silica that comes in a variety of colors, most commonly red, yellow, brown, green, and very rarely blue. It is made mostly of very fine-grained quartz or chalcedony, with other minerals contributing to its color and appearance. The common reddish color is due to iron 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, jewelry, 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.