What is Chromite?
Chromite is the principal chromium-bearing mineral, a dark spinel-group oxide found in ultramafic rocks and important both geologically and industrially.
Mineralogy and structure
The reference formula is FeCr2O4. Chromite belongs to the oxides and has a cubic crystal system. The cubic spinel structure allows substitution between iron, magnesium, chromium and aluminium. Well-formed crystals are uncommon; massive granular ore is more typical than gem-quality material.
Colour and appearance
Typical colours include black, brownish black, dark brown. Crystal habit, lustre, transparency and matrix association are often as diagnostic as colour.
Formation and localities
Chromite forms in or is associated with layered mafic intrusions, podiform bodies and serpentinised ultramafic rocks. Important documented localities include South Africa, Zimbabwe, Turkey, Kazakhstan, the Philippines and the United States.
Collecting and care
Chromite is best kept as a labelled collector or reference specimen. Protect fragile crystals from impact and prolonged humidity changes. Lead-, arsenic-, chromium- and cobalt-bearing minerals should not be cut, ground or used in jewellery.
