One definition of a mineral encompasses the following criteria:
- Formed by a natural process (
anthropogenic compounds are excluded).
Stable or metastable at
room temperature (25 °C). In the simplest sense, this means the mineral must be solid. Classical examples of exceptions to this rule include native
mercury, which crystallizes at −39 °C, and water ice, which is solid only below 0 °C; because these two minerals were described before 1959, they were grandfathered by the
International Mineralogical Association (IMA).
 Modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy.
- Represented by a
chemical formula. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution; pure substances are not usually found because of contamination or chemical substitution. For example, the
olivine group is described by the variable formula (Mg, Fe)2SiO4, which is a solid solution of two end-member species, magnesium-rich
forsterite and iron-rich
fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable compositions, such as the sulfide
mackinawite, (Fe, Ni)9S8, which is mostly a ferrous sulfide, but has a very significant nickel impurity that is reflected in its formula.
- Ordered atomic arrangement. This generally means
crystalline, however, crystals are also periodic, so the broader criterion is used instead.
 An ordered atomic arrangement gives rise to a variety of
macroscopic physical properties, such as crystal form, hardness, and cleavage.
 There have been several recent proposals to classify biogenic or
amorphous substances as minerals. The formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes."
abiogenic (not resulting from the activity of living organisms). Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced entirely by biological processes without a geological component (e.g., urinary calculi, oxalate crystals in plant tissues, shells of marine molluscs, etc.) and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound, then the product can be accepted as a mineral."
The first three general characteristics are less debated than the last two.
Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the
Strunz classification schemes.
 The organic class includes a very rare group of minerals with
hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names.
 According to these new rules, "mineral species can be grouped in a number of different ways, on the basis of chemistry, crystal structure, occurrence, association, genetic history, or resource, for example, depending on the purpose to be served by the classification."
The Nickel (1995)
 The distinction is a matter of classification and less to do with the constituents of the minerals themselves. Skinner (2005) views all solids as potential minerals and includes
biominerals in the mineral kingdom, which are those that are created by the metabolic activities of organisms. Skinner expanded the previous definition of a mineral to classify "element or compound, amorphous or crystalline, formed through
biogeochemical processes," as a mineral.
exclusion of biogenic substances was not universally adhered to. For example, Lowenstam (1981) stated that "organisms are capable of forming a diverse array of minerals, some of which cannot be formed inorganically in the biosphere."
Recent advances in high-resolution
X-ray absorption spectroscopy are providing revelations on the biogeochemical relations between
microorganisms and minerals that may make Nickel's (1995) biogenic mineral exclusion obsolete and Skinner's (2005) biogenic mineral inclusion a necessity.
 For example, the IMA commissioned "Environmental Mineralogy and Geochemistry Working Group"
 deals with minerals in the
biosphere. The group's scope includes
mineral-forming microorganisms, which exist on nearly every rock, soil, and particle surface spanning the globe to depths of at least 1600 metres below the
sea floor and 70 kilometres into the
stratosphere (possibly entering the
Biogeochemical cycles have contributed to the formation of minerals for billions of years. Microorganisms can
precipitate metals from
solution, contributing to the formation of
ore deposits. They can also
dissolution of minerals.
Prior to the International Mineralogical Association's listing, over 60 biominerals had been discovered, named, and published.
 These minerals (a sub-set tabulated in Lowenstam (1981)
) are considered minerals proper according to the Skinner (2005) definition.
 These biominerals are not listed in the International Mineral Association official list of mineral names,
 however, many of these biomineral representatives are distributed amongst the 78 mineral classes listed in the Dana classification scheme.
 Another rare class of minerals (primarily biological in origin) include the mineral
liquid crystals that have properties of both liquids and crystals. To date over 80,000 liquid crystalline compounds have been identified.
The Skinner (2005) definition of a mineral takes this matter into account by stating that a mineral can be crystalline or amorphous, the latter group including liquid crystals.
 Although biominerals and liquid mineral crystals, are not the most common form of minerals,
 they help to define the limits of what constitutes a mineral proper. The formal Nickel (1995) definition explicitly mentioned crystallinity as a key to defining a substance as a mineral. A 2011 article defined
icosahedrite, an aluminium-iron-copper alloy as mineral; named for its unique natural
icosahedral symmetry, it is a
quasicrystal. Unlike a true crystal, quasicrystals are ordered but not periodic.
Rocks, ores, and gems
Minerals are not equivalent to rocks. A
rock is an aggregate of one or more minerals
 or mineraloids. Some rocks, such as
quartzite, are composed primarily of one mineral—
aragonite in the case of limestone, and
quartz in the latter case.
 Other rocks can be defined by relative abundances of key (essential) minerals; a
granite is defined by proportions of quartz,
alkali feldspar, and
 The other minerals in the rock are termed accessory, and do not greatly affect the bulk composition of the rock. Rocks can also be composed entirely of non-mineral material;
coal is a sedimentary rock composed primarily of organically derived carbon.
In rocks, some mineral species and groups are much more abundant than others; these are termed the rock-forming minerals. The major examples of these are quartz, the
olivines, and calcite; except the last one, all of the minerals are silicates.
 Overall, around 150 minerals are considered particularly important, whether in terms of their abundance or aesthetic value in terms of collecting.
Commercially valuable minerals and rocks are referred to as
industrial minerals. For example,
muscovite, a white mica, can be used for windows (sometimes referred to as isinglass), as a filler, or as an insulator.
Ores are minerals that have a high concentration of a certain element, typically a metal. Examples are
cinnabar (HgS), an ore of mercury,
sphalerite (ZnS), an ore of zinc, or
cassiterite (SnO2), an ore of tin.
Gems are minerals with an ornamental value, and are distinguished from non-gems by their beauty, durability, and usually, rarity. There are about 20 mineral species that qualify as gem minerals, which constitute about 35 of the most common gemstones. Gem minerals are often present in several varieties, and so one mineral can account for several different gemstones; for example,
sapphire are both
Nomenclature and classification
Minerals are classified by variety, species, series and group, in order of increasing generality. The basic level of definition is that of mineral species, each of which is distinguished from the others by unique chemical and physical properties. For example, quartz is defined by its
formula, SiO2, and a specific
crystalline structure that distinguishes it from other minerals with the same chemical formula (termed
polymorphs). When there exists a range of composition between two minerals species, a mineral series is defined. For example, the
biotite series is represented by variable amounts of the
eastonite. In contrast, a mineral group is a grouping of mineral species with some common chemical properties that share a crystal structure. The
pyroxene group has a common formula of XY(Si,Al)2O6, where X and Y are both cations, with X typically
bigger than Y; the pyroxenes are single-chain silicates that crystallize in either the
monoclinic crystal systems. Finally, a mineral variety is a specific type of mineral species that differs by some physical characteristic, such as colour or crystal habit. An example is
amethyst, which is a purple variety of quartz.
Two common classifications, Dana and Strunz, are used for minerals; both rely on composition, specifically with regards to important chemical groups, and structure.
James Dwight Dana, a leading geologist of his time, first published his System of Mineralogy in 1837; as of 1997, it is in its eighth edition. The Dana classification assigns a four-part number to a mineral species. Its class number is based on important compositional groups; the type gives the ratio of cations to anions in the mineral; and the last two numbers group minerals by structural similarity within a given type or class. The less commonly used
Strunz classification, named for German mineralogist
Karl Hugo Strunz, is based on the Dana system, but combines both chemical and structural criteria, the latter with regards to distribution of chemical bonds.
As of September 2017
 They are most commonly named after a person (45%), followed by discovery location (23%); names based on chemical composition (14%) and physical properties (8%) are the two other major groups of mineral name etymologies.
 The common suffix -ite of mineral names descends from the ancient Greek suffix – ί τ η ς (-ites), meaning "connected with or belonging to".
, 5,291 mineral species are approved by the IMA.