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Cinnabar

Cinnabar
Cinnabarit 01.jpg
Cinnabar
General
Category Sulfide mineral
Formula
(repeating unit)
Mercury(II) sulfide, HgS
Strunz classification 2.CD.15a
Crystal system Trigonal
Crystal class Trapezohedral (32)
(same H-M symbol)
Space group P3121, P3221
Unit cell a = 4.145(2) Å, c = 9.496(2) Å, Z = 3
Identification
Color Cochineal-red, towards brownish red and lead-gray
Crystal habit Rhombohedral to tabular; granular to massive and as incrustations
Twinning Simple contact twins, twin plane {0001}
Cleavage Prismatic {1010}, perfect
Fracture Uneven to subconchoidal
Tenacity Slightly sectile
Mohs scale hardness 2.0-2.5
Luster Adamantine to dull
Streak Scarlet
Diaphaneity Transparent in thin pieces
Specific gravity 8.176
Optical properties Uniaxial (+)
Refractive index nω = 2.905 nε = 3.256
Birefringence δ = 0.351
Solubility 1.04 x 10−25 g per 100 ml water (Ksp at 25°C = 2 x 10−32)
References

Cinnabar (/ˈsɪnəbɑːr/) and cinnabarite (/sɪnəˈbɑːrt/), likely deriving from the Ancient Greek: κιννάβαρι (kinnabari), refer to the common bright scarlet to brick-red form of mercury(II) sulfide, formula 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 ~3.2, a hardness between 2 and 2.5, and a specific gravity of ~8.1. The color and properties derive from a structure that is a rhombohedral crystalline lattice belonging to the hexagonal crystal system, crystals that sometimes exhibit twinning.


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