Heliotrope (mineral)

Heliotrope
A heliotrope, also known as a bloodstone.
General
Category	Mineral
Chemical formula	SiO2 (silicon dioxide)
Identification
Crystal system	Trigonal
Mohs scale hardness	6.5–7
Luster	Vitreous
Specific gravity	2.61
Refractive index	1.53–1.54
Birefringence	0.004

The mineral heliotrope, also known as bloodstone, is a form of chalcedony (which is a cryptocrystalline mixture of quartz and its monoclinic polymorph moganite). The "classic" bloodstone is green chalcedony with red inclusions of iron oxide or red jasper. Sometimes the inclusions are yellow, in which case the mineral is given the name plasma.

The red inclusions are supposed to resemble spots of blood; hence the name "bloodstone". The name "heliotrope" (from Greek ήλιος helios, Sun, τρέπειν trepein, to turn) derives from various ancient notions about the manner in which the mineral reflects light. These are described, e.g., by Pliny the Elder (Nat. Hist. 37.165).

Heliotrope features in one of Boccaccio's stories in the Decameron.

Heliotrope is the traditional birthstone for December.

Sources

The primary source of the stone is India. It is also found in Brazil, China, Australia and the United States. There is also an outcrop of bloodstone on the Isle Of Rum, in Scotland.

References

• Hall, Candy A. (1994). Gem Stones. DK Publishing. ISBN 1-56458-498-4.