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Formula: Hg3S2Cl2
Chloride, paramorph of
kenhsuite and lavrentievite,
mercury-bearing mineral
Crystal System: Isometric
Specific gravity: 6.845 calculated
Hardness: 3
Colour: Light orange-pink, but becomes light grey to black on prolonged exposure to light
Environments
Volcanic igneous environments
Hydrothermal environments
Localities
At the Arzak Hg occurrence, Uyuk Range, Pi-Khem District, Tuva, Russia, corderoite occurs in the oxidised
hydrothermal deposit asssociated with cinnabar,
calomel, eglestonite,
arzakite, lavrentievite,
kuznetsovite, mercury,
quartz and kaolinite
(HOM).
At the Mariquita Mine (Sultana Mine), Usagre, Badajoz, Extremadura, Spain, remarkable corderoite specimens
have been found which may be one of the best occurrences in the world. the corderoite occurs as colourless,
whitish, or yellow dodecahedral crystals to 2 mm in size, usually isolated, with smooth faces lacking the striations
typical of the more common eglestonite. It also has been found as poorly
defined, whitish to yellow or orange crystals in clusters reaching 5 mm, on
quartz or cinnabar.
Corderoite is an early alteration product of cinnabar in
chloride-enriched brines, formed possibly under acidic and mildly oxidising conditions. The more abundant presence
of corderoite and calomel with respect to
mercury is an indicator of the high concentration of chlorine in the brines
during the alteration of primary
cinnabar.
Corderoite darkens quickly when exposed to sunlight, changing colour from white or yellow to orange, then
reverting to yellow in darkness. A longer exposure results in the formation of elemental
mercury, irreversibly changing the colour to grey
(MinRec 55.4.496-497).
Corderoite from the Mariquita Mine -
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At the type locality, the McDermitt mine, Opalite Mining District, Humboldt County, Nevada, USA, corderoite,
with or without cinnabar, occurs predominantly in playa sediments. The lake
sediments consist of clays (altered
tuff and ash) with lesser amounts of
agglomerate and small lenses of
chalcedony. The associated ore zone minerals are mainly pale green to
buff-coloured montmorillonite,
alpha quartz, cristobalite,
K-feldspar and plagioclase
feldspar.
Corderoite occurs in this zone as separate masses or as replacements and rims for
cinnabar, other associated minerals include
kleinite, kenhsuite,
radtkeite, montmorillonite,
quartz, cristobalite,
orthoclase and plagioclase.
Corderoite and cinnabar also occur within hydrothermally altered
rhyolitic breccia in
the main Cordero mine and nearby underground workings and surface pits.
The relative ease with which corderoite is formed under acid conditions, the presence of chlorine ions as a
common constituent of hot spring or groundwaters, and the relationships observed in the field suggest that
corderoite is a low temperature supergene mineral
(AM 59.652-655, HOM).
Corderoite from the McDermitt Mine -
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