Oldhamite

Oldhamite
Oldhamite (field of view: 1.5 cm)
General
Category	Sulfide mineral
Formula (repeating unit)	(Ca,Mg)S
Strunz classification	2.CD.10
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fm3m
Unit cell	a = 5.69 Å; Z = 4
Identification
Color	Pale chestnut-brown
Crystal habit	Crystal nodules, anhedral grains
Cleavage	Good on {001}
Mohs scale hardness	4
Luster	Sub-metallic
Diaphaneity	Transparent
Specific gravity	2.58
Optical properties	Isotropic
Refractive index	n = 2.137
Fusibility	2450 °C
Alters to	Tarnishes on exposure to moist air
References	[1][2][3]

Oldhamite is a calcium magnesium sulfide mineral with the chemical formula (Ca,Mg)S.^[1][2] Ferrous iron may also be present in the mineral resulting in the chemical formula (Ca,Mg,Fe)S.^[3] 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 , Gorakhpur, Uttar Pradesh, India. It was named for Irish geologist Thomas Oldham (1816–1878), the Director of the Indian Geological Survey.^[1][2]

It occurs as an interstitial mineral phase between silicate minerals in enstatite chondrite and achondrite meteorites.^[1][3] It occurs in association with enstatite, augite, niningerite, osbornite, troilite, gypsum and calcite.^[1] 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.^[2]

See also[]

• Glossary of meteoritics

References[]

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