Metacinnabar

minerals

cinnabar

wurtzite

realgar

Formula: HgS
Sulphide, sphalerite group, isometric paramorph of cinnabar (trigonal) and hypercinnabar (hexagonal), forms a series with tiemannite
Specific gravity: 7.7 to 7.8
Hardness: 3
Streak: Black
Colour: Black, grey-black
Environments

Hydrothermal environments

Metacinnabar is found with cinnabar in mercury deposits formed under low-temperature near-surface conditions (Webmin, HOM). Associated minerals include cinnabar, mercury, wurtzite, stibnite, marcasite, realgar, calcite, baryte, chalcedony and hydrocarbons (HOM).

Localities

The type locality is the Redington Mine, Knoxville, Knoxville Mining District, Napa county, California, USA.

At the Huron River Uranium Prospect, Baraga County, Michigan, USA, metacinnabar has been noted on several brecciated quartz-slate specimens (R&M 87.2.136-137).

Alteration

Cinnabar inverts to metacinnabar at 344oC, at one atmosphere pressure. The inversion is comparatively rapid and is reversible for pure HgS. The presence of small amounts of iron, zinc or selenium in the metacinnabar retards the inversion of metacinnabar to cinnabar at temperatures at which cinnabar is stable. Iron, to as low as 305oC, and zinc to as low as 240oC. In ores containing both cinnabar and metacinnabar, in general metacinnabar was deposited earlier than cinnabar. Metacinnabar does not appear to be an alteration product of cinnabar, but some cinnabar is the product of the inversion of metacinnabar (AM 44.471-487, R&M 87.2.136-137).

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