Corderoite is an extremely rare mercury

sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

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 Humboldt County is a county in the U.S. state of Nevada. As of the 2020 Census, the population was 17,285. It is a largely rural county that is sparsely populated with the only major city being Winnemucca which has a population of 8,431. Hum ...

. The name is from the old name of the mine, the ''Old Cordero Mine.''

Structure

The structure of was determined in the 1960s before it was found in nature. It has crankshaft chains that are crosswise linked by additional Hg²+. The crystals are

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

(existing in two enantiomorphic forms), in

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

I23 (no. 199). The chloride ions form a lattice similar to a primitive cubic lattice (but with the ions slightly displaced along three-fold axes), and the sulfide ions form a similar lattice by occupying positions near the centres of the cubes of chloride ions, also on three-fold rotation axes. This gives eight chloride and eight sulfide ions per unit cell. The mercury ions are located on two-fold rotation axes that do not intersect the three-fold rotation axes. They occupy positions close to the centres of the faces of the chloride cubes, but only half of such positions are occupied, giving 12 mercury ions per unit cell. The closest neighbors of a mercury ion are two sulfide ions, at a distance of 2.422 Å, the S-Hg-S angle being 165.1°. Each sulfide ion has three mercury ions near it, with the Hg-S-Hg angles being 94.1°. The nearest neighbors of a chloride ion are six mercury ions, at two somewhat different distances. A diagram can be seen on line, with blue balls representing mercury, green chlorine, and yellow sulfur. Click on "View JMOL 3-D Structure". Various sulfide halides of Hg share the feature of being face-sharing gS₂X₄polyhedral, with X=Cl in the case of corderoite.

Geologic occurrence

The main occurrence of corderoite in the type locality is in the Upper

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

playa sediments within a thick zone, around , sub parallel to bedding. Lake sediments including altered

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...

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.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

References

{{Reflist *Grenchischev O. K. and Vasil'ev V. I. (1978) "First find of Corderoite (Hg₃S₂Cl₂) in mercury ores of USSR". Doklady. 246/1-6, 145. *Keller P., Lissner F., and Schleid T. (2005) "Single-crystal structure determination of Perroudite, Hg₅Ag₄S₅ (I,Br)₂Cl₂, from Tsumeb (Namiba), and its structural relationships to other sulfide halides of mercury and cinnabar." Stuttgart 181/1, 1–9. *Lavrent'ev Y. G. and Vasil'ev V. I. (1986) "New finds and data on the composition of corderoite (Hg₃S₂Cl₂)". ''Soviet Geology and Geophysics'', 27/12, 117–121. *Modreski P. J. (1998) "Eugene Edward Foord, 1946–1998". ''The Canadian Mineralogist'', 36/2, 251–254. Sulfide minerals Chloride minerals Mercury(II) minerals Cubic minerals Minerals in space group 199 Minerals described in 1974