CINNABAR, sometimes written cinnabarite, is red mercuric sulphide (HgS), or native vermilion, the common ore of mercury (Ger. Zinnober). The name comes from the Greek ,avv6.13ape used by Theophrastus, and probably applied to several distinct substances. Cinnabar is generally found in a massive, granular or earthy form, of bright red colour, but it occasionally occurs in crystals, with a metallic adamantine lustre. The crystals belong to the hexagonal system, and are generally of rhombohedral habit, sometimes twinned. Cinnabar presents remarkable resemblance to quartz in its symmetry and optical characters. Like quartz it exhibits circular polarization, and A. des Cloizeaux showed that it possessed 15 times the rotatory power of quartz (see POLARIZA TION OF LIGHT). Cinnabar has higher refractive power than any other known mineral, its mean index for sodium light being 3.02, while the index for diamond is only 2.42 (see REFRACTION). The hardness of cinnabar is 3, and its specific gravity 9. Cinnabar is found in all localities which yield mercury. Hepatic cinnabar is an impure variety from Idria, in which the cinnabar is mixed with bituminous and earthy matter; and metacinnabarite is a cubic form of mercuric sulphide, this compound being dimorphous.