Metacinnabar

Metacinnabar
Metacinnabar collected from Mount Diablo Mine, Mount Diablo, Clayton, California
General
Category	Sulfide mineral
Formula (repeating unit)	HgS
Strunz classification	2.CB.05a
Crystal system	Cubic
Crystal class	Hextetrahedral (43m) H-M symbol: (4 3m)
Space group	F43m
Unit cell	a = 5.8717(5) Å; Z = 4
Identification
Color	Grayish black
Crystal habit	Massive, rarely as tetrahedral crystals, as incrustations
Twinning	Common as lamellae on {111}
Cleavage	None
Fracture	Subconchoidal
Tenacity	Brittle
Mohs scale hardness	3
Luster	Metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	7.7 - 7.8
References

Metacinnabar is the cubic form of mercury sulfide (HgS). It is the low temperature form and trimorphous with cinnabar (trigonal structure) and the high temperature hypercinnabar (hexagonal structure). It occurs with cinnabar in mercury deposits and is associated with native mercury, wurtzite, stibnite, marcasite, realgar, calcite, barite, chalcedony and hydrocarbons.

It was first described in 1870 for an occurrence in the Redington mine, Knoxville, Napa County, California.