Corderoite

Corderoite

Dark red bands of cinnabar alternate with layers of tan limonite. The corderoite are the yellow-tan microcrystals.
General
Category Halide mineral
Formula
(repeating unit)		 Hg3S2Cl2
Strunz classification 02.FC.15a
Crystal system Cubic - Diploidal
Unit cell a = 8.940(5) Å, Z=4
Identification
Color Pale orange-pink to salmon-pink; on exposure to light, rapidly darkening to pale gray, then black
Crystal habit Rare as cubic crystals; as rims and replacements of cinnabar
Crystal symmetry Isometric 2/m3
Mohs scale hardness 3
Diaphaneity Transparent
Specific gravity 6.845 calc.
Optical properties Isotropic
Refractive index n > 2.5
References [1][2][3]

Corderoite is an extremely rare mercury sulfide chloride mineral with formula Hg3S2Cl2. It crystallizes in the isometric crystal system. It is soft, 1.5 to 2 on the Mohs scale, and varies in color from light gray to black and rarely pink or yellow.

It was first described in 1974 for occurrences in the McDermitt Mercury mine in Humboldt County, Nevada. The name is from the old name of the mine, the Old Cordero Mine.[4]

Structure

Corderoite has crankshaft chains that are crosswise linked by additional Hg²+. The bond distance between the cation Hg and anion S is 2.422 Angstroms. It has two angles, Hg-S-HG= 94.1º and S-Hg-S= 165.1º. Various sulfide halides of Hg share the feature of being face-sharing [HgS2X4] −6 polyhedral, as corderoite's polyhedra X=Cl.

Geologic occurrence

The main occurrence of corderoite in the type locality is in the Upper Miocene playa sediments within a thick zone, around 5–7 m (16–23 ft), sub parallel to bedding. Lake sediments including altered rhyolitic tuff and ash were deposited on the Tertiary rhyolitic volcanic rocks. Corderoite occurs as isolated grains or with cinnabar as replacements. Corderoite occurs as a low temperature supergene mineral.[5]

References

  1. ↑ http://rruff.geo.arizona.edu/doclib/hom/corderoite.pdf Handbook of Mineralogy
  2. ↑ http://www.mindat.org/min-1127.html Mindat with location data
  3. ↑ http://www.webmineral.com/data/Corderoite.shtml Webmineral data
  4. ↑ http://www.mindat.org/loc-4206.html Mindat McDermii Mine page
  5. ↑ Berendsen P., Foord E. E., and Storey L. O. (1974) "Corderoite, first natural occurrence of Hg3S2Cl2, from the Cordero mercury deposit, Humboldt County, Nevada". American Mineralogist, 59, 652–655 http://www.minsocam.org/ammin/AM59/AM59_652.pdf
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