Cinnabar: Gemstones Information
Cinnabar is HgS and forms rare cochineal-red translucent rhombohedral crystals of the trigonal system with an adamantine to metallic lustre;masses and encrustations are more common. There is one direction of perfect cleavage, the hardness is 2–2.5 and the SG 8.20. The RI for the ordinary and extraordinary rays is 2.905 and 3.25, uniaxial positive with birefringence 0.351. Cinnabar occurs in low-temperature ore deposits and is also found in veins and around hot springs. Cinnabar crystals,some of which may be faceted, usually come from a notable deposit at the Tsar Tien mine, Hunan Province, China.