Usually refers to a chemical reaction in which an element combines with oxygen (usually in air or water). For instance, rusting is an oxidation reaction: iron oxidizes, that is it combines with oxygen, to form iron-oxides.

The most common mineral on earth.

Quartz-rich sandstone that has been metamorphosed.

An exposure of rock along a road, created when the road was excavated.

A hard, solid mass composed of one or more minerals or other compounds.