"Cinnabar (/ˈsɪnəˌbɑːr/) or cinnabarite (/sɪnəˈbɑːraɪt/), likely deriving from the Ancient Greek: κιννάβαρι (kinnabari), is the bright scarlet to brick-red form of mercury(II) sulfide (HgS). It is ...
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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 near 3.2, a hardness between 2.0 and 2.5, and a specific gravity of approximately 8.1. The color and properties derive from a structure that is a hexagonal crystalline lattice belonging to the trigonal crystal system, crystals that sometimes exhibit twinning." - (en.wikipedia.org 14.10.2021)