Plasma Chalcedony is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of silicon dioxide, their full chemical compound being SiO2.
Plasma is a massive, semitransparent, leek to dark green variety of Chalcedony (a microcrystalline variety of the Quartz group), microgranular or microfibrous, consisting of speckles of red or brownish-red jasper, resembling drops of blood.
It is translucent to opaque, may be dark green to bright-green, apple-green, or nearly emerald-green, containing microfibrous of actinolite, frequently flecked with white or yellowish spots. Those with red spots are known as bloodstone. Particles of various silicate minerals (chiefly of the chlorite group) disseminated through which may be varied by the presence of white or yellowish patches. Its green color caused by chlorite. The colors are not always constant.
Plasma is also called heliotrope (its old name) and bloodstone jasper.
Brazil, Australia, India, Madagascar, Egypt, South Africa, the northwestern states of the USA, have commercial deposits of plasma.
The names heliotrope, now hardly used, and bloodstone, still in common use, are used for a type of chalcedony or plasma with spots of iron oxide or red jasper resembling blood spots against a dark green background. Good-quality material comes from the Deccan trap-rocks, India, from Brazil and many other countries.
The specific gravity [?] for Plasma Chalcedony is 2.61, it's refractive index [?] is 1.53-1.54, and it's double refraction [?] is 0.004.
During the Middle Ages, special magic powers were ascribed to plasma with red spots, as the spots were thought to be drops of Christ's blood.
Plasma is often used in signet rings, carved objects and amulets.
It has been used in imitation of jade, along with several varieties of quartz which include other green varieties of chalcedony, chrysoprase and also green aventurine quartz (otherwise known as Indian jade), which is coloured by inclusions of the chromian muscovite mica, fuchsite.