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Oldhamite (field of view: 1.5 cm)
Category Sulfide mineral
(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
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 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]