Mineral
A naturally occurring inorganic solid with a definite chemical composition and an ordered crystal structure.
Unit
Dimensionless
In depth
Minerals are the building blocks of rocks and are identified by hardness, cleavage, colour, streak and crystal habit as well as by X-ray diffraction. A mineral becomes an ore only when it contains enough of a wanted metal to justify extraction.
Examples in the real world
Quartz, calcite, feldspar and pyrite; clay minerals is a general term for a whole structural family.