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Formula: Sb2S3
Valence: Sb3+2S2-3
Simple sulphide of antimony, amorphous
paramorph of orthorhombic
stibnite
Crystal system: Amorphous
Hardness: 2 to 3
Streak: Red
Colour: Red, reddish brown, purplish, intense red internal reflections
Environments
Hydrothermal environments
Fumeroles
Localities
At the Alacrán Mine, Alacrán, Pampa Larga mining district, Tierra Amarilla, Copiapó Province, Atacama, Chile,
metastibnite occurs as an oxidation product of stibnite. It was
found as a reddish-brown powdery coating on stibnite in a specimen from
the dumps of the mine. The coating occurs in fractures in bladed stibnite
aggregates, associated with minor, massive cinnabar in a
baryte gangue.
It may be noted that stibnite, a major constituent of the Alacrán veins,
here coexists with realgar,
orpiment and native arsenic, and
contains up to 0.6 weight per cent As in the earliest vein assemblages, while the later-formed
stibnite, such as that associated with the metastibnite, is
essentially arsenic-free
(AM 55.2104-2106).
At the Big Geyser property, The Geysers, West Mayacmas Mining District, Sonoma County, California, USA, bulldozing
operations through a bank of siliceous sinter revealed rocks stained red by what was thought to be
cinnabar, but subsequently found to be metastibnite. The red
material occurs as coatings in cracks in siliceous sinter but nowhere is observed to form a complete vein.
The conditions necessary for the formation of metastibnite are not clear. Metastibnite at Mina Alacrán
has been attributed to oxidation from stibnite, but the
metastibnite found at The Geysers and at Steamboat Springs may be
primary. The data suggest that a gas phase, probably
H2S, is involved in the formation of primary
metastibnite. This explanation would also account for its occurring as coatings in cracks but not as complete
veins
(AM 55.2103-2104).
At the type locality, Steamboat Hot Springs, Steamboat Springs Mining District, Washoe County, Nevada, USA,
metastibnite occurs as stains, mammilary and powdery coatings, and impregnations of siliceous sinter. It is
of primary hydrothermal origin around fumarolic centres,
associated with cinnabar
(Mindat).
Metastibnite from Steamboat Hot Springs -
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