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Category Sulfide mineral
(repeating unit)
(Ca, Mg)S
Strunz classification 2.CD.10
Crystal symmetry Isometric hexoctahedral
H-M symbol: (4/m32/m)
Space group: F m3m
Unit cell a = 5.69 Å; Z=4
Color Pale chestnut-brown
Crystal habit Crystal nodules, anhedral grains
Crystal system Cubic
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 formula (Ca, Mg)S.[1][2] Ferrous iron may also be present in the mineral resulting in the 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[edit]

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.[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[edit]