Carnelian
| Carnelian | |
|---|---|
| General | |
| Category | Tectosilicate minerals |
| Group | Quartz group |
| Formula | SiO2 (silicon dioxide) |
| IMA status | Variety of quartz (chalcedony) |
| Crystal system | Trigonal (quartz), monoclinic (moganite) |
| Identification | |
| Formula mass | 60 g/mol |
| Color | Reddish, orange, brownish |
| Cleavage | Absent |
| Fracture | Uneven, splintery, conchoidal |
| Mohs scale hardness | 6.5–7.0 |
| Luster | Waxy to resinous |
| Streak | White |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 2.58–2.64 |
| Optical properties | Uniaxial + |
| Refractive index | 1.535–1.539 |
| Birefringence | 0.003–0.009 |
| References | |
Carnelian (also spelled cornelian) is a brownish-red mineral commonly used as a semiprecious stone. Similar to carnelian is sard, which is generally harder and darker; the difference is not rigidly defined, and the two names are often used interchangeably. Both carnelian and sard are varieties of the silica mineral chalcedony colored by impurities of iron oxide. The color can vary greatly, ranging from pale orange to an intense almost-black coloration. Significant localities include Yanacodo, Peru and Ratnapura, Sri Lanka. It has been found in Indonesia, Brazil, India, Iran, Russia (Siberia), and Germany.