Minerals can be identified and distinguished by various physical
properties and by ascertaining their chemical composition. The chief
distinguishing physical properties are crystalline form, cleavage,
hardness, and specific gravity.
Each mineral or special class of minerals has its own definite
geometrical shape or crystalline form. The crystals of each mineral have
also a tendency to break or cleave most readily in a particular
direction. The term hardness, as applied to minerals and other solid
bodies, is used to indicate resistance to being scratched or the power
to scratch. The harder of two bodies is the one which will scratch the
other, and which resists being scratched by that other.