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A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids. The study of minerals is called mineralogy.
There are over 5,300 known mineral species; over 5,070 of these have been approved by the International Mineralogical Association (IMA). The silicate minerals compose over 90% of the Earth's crust. The diversity and abundance of mineral species is controlled by the Earth's chemistry. Silicon and oxygen constitute approximately 75% of the Earth's crust, which translates directly into the predominance of silicate minerals.
Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, which were determined by the mineral's geological environment when formed. Changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals.
Minerals can be described by their various physical properties, which are related to their chemical structure and composition. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, and specific gravity. More specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid.
|Crystal family||Lengths||Angles||Common examples|
|Isometric||a=b=c||α=β=γ=90°||Garnet, halite, pyrite|
|Tetragonal||a=b≠c||α=β=γ=90°||Rutile, zircon, andalusite|
|Orthorhombic||a≠b≠c||α=β=γ=90°||Olivine, aragonite, orthopyroxenes|
|Hexagonal||a=b≠c||α=β=90°, γ=120°||Quartz, calcite, tourmaline|
|Monoclinic||a≠b≠c||α=γ=90°, β≠90°||Clinopyroxenes, orthoclase, gypsum|
|Triclinic||a≠b≠c||α≠β≠γ≠90°||Anorthite, albite, kyanite|
|Mohs hardness||Mineral||Chemical formula|
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