Oldhamite

Rocksalt group, sulfide mineral
(Ca,Mg)SIMA symbolOld[1]Strunz classification2.CD.10Crystal systemCubicCrystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)Space groupFm3mUnit cella = 5.69 Å; Z = 4IdentificationColorPale chestnut-brownCrystal habitCrystal nodules, anhedral grainsCleavageGood on {001}Mohs scale hardness4LusterSub-metallicDiaphaneityTransparentSpecific gravity2.58Optical propertiesIsotropicRefractive indexn = 2.137Fusibility2450 °CAlters toTarnishes on exposure to moist airReferences[2][3][4]

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.

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. ^ a b c d e Handbook of Mineralogy
  3. ^ a b c d Oldhamite on Mindat.org
  4. ^ a b c Webmineral dat for oldhamite
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