A mineral, by definition, is a naturally occurring chemical element or compound, inorganically formed. Thus, a mineral may be a single element, such as gold, or a chemical compound, such as fluorite (calcium fluoride) and quartz (silicon dioxide). The arrangement of atoms in a mineral is ordered, which defines the crystalline state. Minerals may occur in various forms - as perfect crystals or as aggregates of many imperfect crystals.

All minerals belong to a chemical group, which represents their affiliation with certain elements or compounds. The classified chemical groups are known as: Elements, Sulfides, Oxides, Halides, Carbonates, Nitrates, Borates, Sulfates, Chromates, Phosphates, Arsenates, Vanadates, Tungstates, Molybdates, and Silicates. Some of these chemical groups have sub-categories, which may be categorized in some mineral references as separate groups.

Minerals belong to various crystal systems, classified by which the atoms of the mineral are arranged. Minerals also have distinctive properties, such as color, streak, luster, diaphaneity, specific gravity (density), hardness, cleavage, fracture, and morphology. Many of these properties can vary among a single mineral, within limits. Many minerals exhibit certain properties that others do not, such as fluorescence and radioactivity.

Some minerals are mined because of the need for a valuable element they contain or an intrinsic property they may have. Other minerals are mined for their beauty and rareness, thus giving many specimens an accepted worldwide value. There are about 4,500 different types of minerals, and new ones are constantly discovered. Most of them are not known to professional mineral collectors, because they are rare, have no economic purpose, and for the most part do not make good collection specimens.