A heliotrope, also known as a bloodstone.
|SiO2 (silicon dioxide)|
|Color||Green with red or yellow spots|
|Mohs scale hardness||6.5–7|
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 ἥλιος 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 is sometimes used in carved signet rings and is the traditional birthstone for March.
- Hall, Candy A. (1994). Gem Stones. DK Publishing. ISBN 1-56458-498-4.
- "heliotrope". Merriam-Webster Dictionary. m-w.com.
- Media related to Heliotrop at Wikimedia Commons