Oxide
An oxide is a mineral in which a metal is combined directly with oxygen, such as chromite or magnetite.
An oxide is a mineral made of one or more metals joined to oxygen, without silicon. Familiar examples are haematite and magnetite, both iron oxides, and corundum, an aluminium oxide.
In meteorites, oxides are minor but telling. Chromite, an iron chromium oxide, is the commonest and survives weathering so well that fossil chromite grains from meteorites that fell some 470 million years ago have been found in ancient limestone in Sweden. Magnetite appears in carbonaceous chondrites, often formed by water reacting with metal. Ilmenite, an iron titanium oxide, occurs in lunar basalts and eucrites, and spinel, perovskite and corundum appear in CAIs.
Oxides help reveal the oxygen conditions in which a rock formed. Their chemistry can also be used as thermometers. On Earth's surface, iron in fallen meteorites slowly turns into iron oxides and hydroxides, which is the rust that eventually destroys them.
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Level: Explorer Ages 10 and up