BLOODSTONE or HELIOTROPE is a dark-green variety of crypto-crystalline silica, having bright-red nodules distributed throughout its mass. Polished sections therefore show red spots on a dark-green background and, from the resemblance of these to drops of blood, it derives its name. The word heliotrope is de rived from the Greek (Helios, the sun; trope, a turning) and related to one of its supposed properties described by Marbodus in the following lines :— The Heliotrope or "gem that turns the sun," From its strange power the name has justly won: For set in water opposite his rays, As red as blood 'twill turn bright Phoebus' blaze.
It was greatly prized in the middle ages and used in sculptures representing flagellation and martyrdom; it is of small importance now. On heating, the red spots turn black and the green back ground changes to grey.
See C. W. King, Antique Gems (186o) ; Max Bauer, Precious Stones, trans. L. J. Spencer (i904)• (W. A. W.)