Plasma,

Plasma, a rare siliceous mineral, a variety of quartz or chalcedony, of a dark-green colour, black when unpolished and seen by reflected light, but very translucent when held between the eye and the light. It is very nearly allied to heliotrope or bloodstone, but has no red spots, is more translucent, and is not susceptible of so brilliant a polish. The name is also used in biology for the simplest form of organised matter in vegetable and animal bodies, out of which the tissues are formed, especially of the blood-plasma. See BLOOD.