Heliotrope (mineral)
| Heliotrope | |
|---|---|
A tumble-polished pebble of heliotrope, also called bloodstone | |
| General | |
| Category | Tectosilicate minerals, quartz group, chalcedony variety |
| Formula | SiO2 (silicon dioxide) |
| Crystal system | Trigonal (quartz), monoclinic (moganite) |
| Identification | |
| Color | Dark shades of green, often with red or yellow spots; sometimes mixed with whitish silica |
| Fracture | Conchoidal |
| Mohs scale hardness | 6.5–7 |
| Luster | Vitreous |
| Diaphaneity | Opaque to translucent |
| Specific gravity | 2.61 |
| Refractive index | 1.53–1.54 |
| Birefringence | 0.004 |
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Heliotropes (from Ancient Greek ἥλιος (hḗlios) 'sun' and τρέπειν (trépein) 'to turn') (also called ematille, Indian bloodstones, or simply bloodstones) are aggregate minerals, and a cryptocrystalline mixture of quartz that occurs mostly as jasper (opaque) or sometimes as chalcedony (translucent).
The "classic" bloodstone is translucent to opaque green chalcedony and red jasper that contains inclusions of hematite. The red jasper may resemble spots of blood, hence the name bloodstone. Other colors of chalcedony may also occur in Indian bloodstone, such as white, yellow, or blue.
This semiprecious stone should not be confused with other ornamental stones that contain red jasper. Setonite, also called African bloodstone, is composed of red jasper, grey chalcedony, and pyrite. Dragon's Blood, sometimes called Australian bloodstone, is composed of red jasper and green epidote.
The name heliotrope derives from ancient beliefs about the manner in which the mineral reflects light. Such notions are described, for example, by Pliny the Elder (Nat. Hist. 37.165).
In the Tropical zodiac, heliotrope is the birthstone for the Astrological sign of Aries.