HgS
Hexagonal -- Trapezohedral
Environment
In shallow veins and rock impregnations, very often in a quartzite (Almaden, Spain) or serpentine (California).
Crystal description
Well-individualized crystals are rare, crystallized crusts and complex intergrowths fairly common. Twinned intergrowths of steep rhombohedrons found at several localities. Also massive, powdery, and granular, sometimes in capillary needles.
Physical properties
Bright red to brick red to almost black.
Luster
adamantine;
hardness
2Ɖ;
specific gravity
8.1;
fracture
subconchoidal;
streak
red;
cleavage
very perfect prismatic. Easily bruised and crushed; translucent to transparent.
Composition
Mercuric sulfide (86.2% Hg, 13.8% S).
Tests
Volatilizes completely on charcoal. In open tube produces sulfur fumes; forms black ring and above this a thin deposit of metallic droplets. This "mercury mirror" can be resolved into drops by scratching over its surface with a needle.
Distinguishing characteristics
Likely to be confused with realgar, cuprite, and possibly "ruby jack" sphalerite or hematite. Easily distinguished by the open-tube test.
Occurrence
Cinnabar, the only ore of mercury, is deposited by epithermal ascending solutions (those near surface and not too hot) far removed from their igneous source. It is associated with native mercury, stibnite, realgar, opal, quartz, and barite. The richest occurrences are on Mt. Avala, Idria, near Belgrade, Serbia; Almadén, Spain; Italy; and Mexico. Historically, the best crystals, including the penetrating rhombohedron type, have been found as scattered individuals up to 2 in. (4-5 cm) in a white calcite matrix in Hunan Province, China. Loose 1-2 in. (3-6 cm) crystals come from the Nikitovka Mine in Ukraine. Briefly, in the late 1920s, the Kirby Mine, Pike Co., Arkansas, had good twins on an iron-stained quartz matrix and enclosed in quartz crystals with hairs of stibnite. Waterworn cinnabar nuggets are found in the Tempati River, Surinam. American deposits are not extensive; the best are in California, with one in Alaska. Smaller quantities have been found in Nevada.