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Cinnabar Mineral Facts:

Chemical Formula: HgS  The Mineral is 86.2% Mercury by weight.

Colors: Red
Vermilion-red when pure, to brownish red when impure. Scarlet streak. Transparent to opaque.

Hardness: 2 to 2.5

Density: 8.1

Cleavage: {1010} perfect

Crystallography: Hexagonal - Rhombohedral
Crystals are usually rhombodedral, often in penetration twins. Trapezohedral faces are rare. Cinnabar is usually fine grained and massive; also earthy and as incrustations. Crystals are rare.

Luster:. Adamantine luster when pure, to dull and earthy when impure.

Optics: (Refractive Index): = 3.2

Composition, Structure and Associated Minerals:
Cinnabar is the only compound of mercury that occurs in sufficient quantity to constitute an important ore. Nearly all of the mercury, or quicksilver, in the world is obtained from it. The mineral occurs both crystallized and massive.  Massive cinnabar is, however, usually impure through the admixture of clay, iron oxides or bituminous substances. Occasionally the quantity of organic material present is so large that the mixture is inflammable. Though cinnabar is usually granular, massive or earthy, it sometimes occurs beautifully crystallized in small complex and highly modified hexagonal crystals that exhibit tetartohedral forms (trigonal trapezohedral class). Usually the crystals are rhombohedral or prismatic in habit.

Identification and Diagnostics
Recognized usually by color, streak and high specific gravity. The mineral is slightly sectile. It is transparent, translucent or opaque, is of a cochineal-red color, often inclining to brown. From all red minerals but realgar it may easily be distinguished by its sulfur reaction. From realgar it is distinguished by its great density and its greater hardness. Wholly volatile when free from gangue. Gives black sublimate of mercury sulfide when heated alone in closed tube. The ore is a red crystalline mass that is easily distinguished from all other red minerals by its peculiar shade of color and its great weight. It is circularly polarizing and is a nonconductor of electricity.

Occurrence, Localities and Origins:
The only important ore of mercury, but found in quantity at comparatively few localities. Cinnabar is usually found in veins cutting serpentine, limestones, slates, shales and various schists. It is associated with gold, various sulfides, especially pyrite and marcasite, calcite , barite, fluorite, gypsum, opal, and quartz. It is also found impregnating sandstones and other sedimentary rocks, and sometimes as a deposit from hot springs. Always found in the neighborhood of igneous rock masses from which it is thought that the mercury was derived. Its deposition is thought to be the result of precipitation from ascending hot water. Deposits of cinnabar are being formed to-day by the hot springs at Steamboat Springs, Nevada, and at Ohaiawai, New Zealand.

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Cinnabar Crystals, Nevada

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