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Formula: HgS
Sulphide, sphalerite group, isometric
paramorph of
cinnabar (trigonal) and hypercinnabar
(hexagonal), forms a series with tiemannite
Crystal System: Isometric
Specific gravity: 7.65 measured, 7.63 calculated
Hardness: 3
Streak: Black
Colour: Black, grey-black
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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