Cinnabar Cinnabar Cinnabar () and cinnabarite (), likely deriving from the ("kinnabari"), refer to the common bright scarlet to brick-red form of mercury(II) sulfide (HgS) that is the most common source ore for refining elemental mercury, and is the historic source for the brilliant red or scarlet pigment termed vermilion and associated red mercury pigments. Cinnabar generally occurs as a vein-filling mineral associated with recent volcanic activity and alkaline hot springs. The mineral resembles quartz in symmetry and in its exhibiting birefringence; cinnabar has a mean refractive index of approximately 3.2, a hardness between 2.0 and 2.5, and a specific gravity
Cinnabar any mineral. Its mean refractive index is 3.08 (sodium light wavelengths), versus the indices for diamond and the non-mineral gallium(III) arsenide (GaAs), which are 2.42 and 3.93, respectively. The hardness of cinnabar is 2.0–2.5 on the Mohs scale, and its specific gravity 8.1. Structurally, cinnabar belongs to the trigonal crystal system. It occurs as thick tabular or slender prismatic crystals or as granular to massive incrustations. Crystal twinning occurs as simple contact twins. Note, mercury(II) sulfide, HgS, adopts the cinnabar structure described, and one additional structure, i.e. it is dimorphous. Cinnabar is the more stable form, and is a structure