oldhamite

{{infobox mineral | name = Oldhamite | boxwidth = | boxbgcolor = | image = Oldhamite-510145.jpg | imagesize = | alt = | caption = Oldhamite (field of view: 1.5 cm) | category = Sulfide mineral | formula = | IMAsymbol = Old | strunz = 2.CD.10 | dana = | system = Cubic | class = Hexoctahedral (mm) H-M symbol: (4/m 2/m) | symmetry = Fmm | unit cell = a = 5.69 Å; Z = 4 | color = Pale chestnut-brown | habit = Crystal nodules, anhedral grains | twinning = | cleavage = Good on {001} | fracture = | tenacity = | mohs = 4 | luster = Sub-metallic | streak = | diaphaneity = Transparent | gravity = 2.58 | density = | polish = | opticalprop = Isotropic | refractive = n = 2.137 | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = 2450 °C | diagnostic = | solubility = | impurities = | alteration = Tarnishes on exposure to moist air | other = | prop1 = | prop1text = |references = }} Oldhamite is a calcium magnesium sulfide mineral with the chemical formula . Ferrous iron may also be present in the mineral resulting in the chemical formula . 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.