Heliotrope (mineral)

Heliotrope
A tumble-polished pebble of heliotrope, also called bloodstone
General
Category	Silicate mineral
Formula (repeating unit)	SiO2 (silicon dioxide)
Crystal system	Trigonal
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

The mineral aggregate heliotrope (from Ancient Greek ἥλιος (hḗlios) 'sun' and τρέπειν (trépein) 'to turn'), also called Indian bloodstone or ematille, is 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).^[1]