Oldhamite

Oldhamite is a calcium magnesium sulfide mineral with the chemical formula (Ca,Mg)S.[2][3] Ferrous iron may also be present in the mineral resulting in the chemical formula (Ca,Mg,Fe)S.[4] It is a pale to dark brown accessory mineral in meteorites. It crystallizes in the cubic crystal system, but typically occurs as anhedral grains between other minerals.

Oldhamite
Oldhamite (field of view: 1.5 cm)
General
CategorySulfide mineral
Formula
(repeating unit)		(Ca,Mg)S
IMA symbolOld[1]
Strunz classification2.CD.10
Crystal systemCubic
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupFm3m
Unit cella = 5.69 Å; Z = 4
Identification
ColorPale chestnut-brown
Crystal habitCrystal nodules, anhedral grains
CleavageGood on {001}
Mohs scale hardness4
LusterSub-metallic
DiaphaneityTransparent
Specific gravity2.58
Optical propertiesIsotropic
Refractive indexn = 2.137
Fusibility2450 °C
Alters toTarnishes on exposure to moist air
References[2][3][4]

Discovery and occurrence

It was first described in 1862 for an occurrence in the Bustee meteorite, Gorakhpur, Uttar Pradesh, India. It was named for Irish geologist Thomas Oldham (1816–1878), the Director of the Indian Geological Survey.[2][3]

It occurs as an interstitial mineral phase between silicate minerals in enstatite chondrite and achondrite meteorites.[2][4] It occurs in association with enstatite, augite, niningerite, osbornite, troilite, gypsum and calcite.[2] It has been reported from a variety of meteorite locations around the world including the Allan Hills 84001 meteorite of Antarctica. It has also been reported from a slag occurrence in France and a coal deposit in Poland.[3]

See also

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Handbook of Mineralogy
  3. Oldhamite on Mindat.org
  4. Webmineral dat for oldhamite


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