A black mineral of the spinel group that is an oxide of ferrous iron and chromium and belongs to the cubic crystal system.

A compound of oxides of iron, manganese, and zinc, found in brilliant black crystals.

Native proto-sesquioxide of manganese, found in brownish-black tetragonal crystals; pyramidal manganese ore.

Aluminate of iron, found in black octahedral crystals in the Bohemian Forest.

An oxide of iron and manganese, belonging to the spinel group, found at Jakobsberg in Sweden.

A black oxide of zinc and manganese, ZnMn2O4, isostructural with hausmannite and found in New Jersey associated with franklinite and with…

An oxide of copper and arsenic, CuAs2O4, found as soft greenish blue tetragonal crystals.

A blue variety of spinel.

a colourless variety of spinel.

A manganiferous mineral now considered to be identical with vredenbergite.

picotite.

Originally: a mineral, (Mg,Fe)Cr2O4, analogous to chromite (FeCr2O4), with magnesium replacing much of the iron. Now usually: a spinel of the…

= magnesiochromite, n. Also: a magnesiochromite containing no iron, MgCr2O4.

a chromite of magnesium, MgCr2O4, belonging to the spinel group, whose pure form is known only as a synthetic product and which occurs naturally…

A black, magnetic, isometric oxide of nickel and ferric iron, NiFe2O4, belonging to the spinel group.

A mineral of the spinel group, Fe2TiO4, frequently found as lamellæ in magnetite.

A mauve gemstone similar to spinel, having the composition BeMgAl4O8 and a hexagonal crystal structure.

an artificially produced oxide of nickel and aluminium, NiAl2O4.