Crystals of serandite, natrolite, analcime, and aegirine: Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada

A mineral is a naturally occurring chemical compound, [1] usually of crystalline form and abiogenic in origin (not produced by life processes). 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; as of March 2017, over 5,230 of these had been approved by the International Mineralogical Association (IMA). [2] The silicate minerals compose over 90% of the Earth's crust. 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, specific gravity, magnetism, taste or smell, radioactivity, and reaction to acid.

Minerals are classified by key chemical constituents; the two dominant systems are the Dana classification and the Strunz classification. The silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a base unit of a [SiO4]4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions, which gives the shape of a tetrahedron. These tetrahedra can be polymerized to give the subclasses: orthosilicates (no polymerization, thus single tetrahedra), disilicates (two tetrahedra bonded together), cyclosilicates (rings of tetrahedra), inosilicates (chains of tetrahedra), phyllosilicates (sheets of tetrahedra), and tectosilicates (three-dimensional network of tetrahedra). Other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates.


Basic definition

One definition of a mineral encompasses the following criteria: [3]

  1. Formed by a natural process ( anthropogenic compounds are excluded).
  2. 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). [4] [5] Modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy.
  3. 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. [3] [6]
  4. Ordered atomic arrangement. This generally means crystalline, however, crystals are also periodic, so the broader criterion is used instead. [3] An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. [7] 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." [8]
  5. Usually 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." [8]

The first three general characteristics are less debated than the last two. [3]

Recent advances

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. [9] [10] 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. [11] [12] 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." [11]

The Nickel (1995)[ clarification needed] 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." [13] 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. [14]

Recent advances in high-resolution genetics and 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. [8] [14] For example, the IMA commissioned "Environmental Mineralogy and Geochemistry Working Group" [15] deals with minerals in the hydrosphere, atmosphere, and 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 mesosphere). [16] [17] [18] 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 catalyze the dissolution of minerals. [19] [20] [21]

Prior to the International Mineralogical Association's listing, over 60 biominerals had been discovered, named, and published. [22] These minerals (a sub-set tabulated in Lowenstam (1981) [13]) are considered minerals proper according to the Skinner (2005) definition. [14] These biominerals are not listed in the International Mineral Association official list of mineral names, [23] however, many of these biomineral representatives are distributed amongst the 78 mineral classes listed in the Dana classification scheme. [14] 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. [24] [25]

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. [14] Although biominerals and liquid mineral crystals, are not the most common form of minerals, [26] 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. [27] [28]

Rocks, ores, and gems

Schist is a metamorphic rock characterized by an abundance of platy minerals. In this example, the rock has prominent sillimanite porphyroblasts as large as 3 cm (1.2 in).

Minerals are not equivalent to rocks. A rock is either an aggregate of one or more minerals [29] or mineraloids. Some rocks, such as limestone or quartzite, are composed primarily of one mineral— calcite or aragonite in the case of limestone, and quartz in the latter case. [30] [31] Other rocks can be defined by relative abundances of key (essential) minerals; a granite is defined by proportions of quartz, alkali feldspar, and plagioclase feldspar. [32] 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. [29] [33]

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 feldspars, the micas, the amphiboles, the pyroxenes, the olivines, and calcite; except the last one, all of the minerals are silicates. [34] Overall, around 150 minerals are considered particularly important, whether in terms of their abundance or aesthetic value in terms of collecting. [35]

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. [36] 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, ruby and sapphire are both corundum, Al2O3. [37]

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 endmembers phlogopite, siderophyllite, annite, and 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 orthorhombic or 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. [38]

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. [39]

As of March 2017, 5,237 mineral species are approved by the IMA. [2] 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. [38] [40] The common suffix -ite of mineral names descends from the ancient Greek suffix - ί τ η ς (-ites), meaning "connected with or belonging to". [41]

Other Languages
Afrikaans: Mineraal
Alemannisch: Mineral
العربية: معدن
aragonés: Mineral
armãneashti: Mineralu
অসমীয়া: খনিজ পদাৰ্থ
asturianu: Mineral
azərbaycanca: Mineral
বাংলা: খনিজ
Bân-lâm-gú: Khòng-bu̍t
беларуская: Мінерал
беларуская (тарашкевіца)‎: Мінэрал
भोजपुरी: खनिज
български: Минерал
bosanski: Mineral
català: Mineral
čeština: Minerál
chiShona: Muchegwa
Cymraeg: Mwyn
dansk: Mineral
Deutsch: Mineral
eesti: Mineraal
Ελληνικά: Ορυκτό
español: Mineral
Esperanto: Mineralo
euskara: Mineral
فارسی: کانی
français: Minéral
Frysk: Mineraal
Gaeilge: Mianra
galego: Mineral
한국어: 광물
Հայերեն: Միներալ
हिन्दी: खनिज
hrvatski: Minerali
Ilokano: Mineral
Bahasa Indonesia: Mineral
interlingua: Mineral
íslenska: Steind
italiano: Minerale
עברית: מינרל
Basa Jawa: Mineral
ಕನ್ನಡ: ಖನಿಜ
ქართული: მინერალები
қазақша: Минерал
Kiswahili: Madini
Kreyòl ayisyen: Mineral
Кыргызча: Минерал
Latina: Minerale
latviešu: Minerāls
lietuvių: Mineralas
lumbaart: Mineraj
मैथिली: खनिज
македонски: Минерал
മലയാളം: ധാതു
Bahasa Melayu: Mineral
Mirandés: Mineral
монгол: Эрдэс
မြန်မာဘာသာ: တွင်းထွက်ပစ္စည်း
Nederlands: Mineraal
नेपाली: खनिज
नेपाल भाषा: खनिज
日本語: 鉱物
Nordfriisk: Mineraal
norsk: Mineral
norsk nynorsk: Mineral
occitan: Minerau
oʻzbekcha/ўзбекча: Mineral
ਪੰਜਾਬੀ: ਖਣਿਜ
پنجابی: معدنیات
Patois: Minaral
Plattdüütsch: Mineral
polski: Minerał
português: Mineral
Qaraqalpaqsha: Mineral
română: Mineral
Runa Simi: Qiqlla
русиньскый: Мінералы
русский: Минерал
संस्कृतम्: खानिजः
Scots: Meeneral
shqip: Minerali
sicilianu: Minirali
සිංහල: ඛනිජ
Simple English: Mineral
slovenčina: Minerál
slovenščina: Mineral
Soomaaliga: Macdan
српски / srpski: Минерал
srpskohrvatski / српскохрватски: Minerali
Basa Sunda: Mineral
suomi: Mineraali
svenska: Mineral
Tagalog: Mineral
தமிழ்: கனிமம்
తెలుగు: మినరల్
ไทย: แร่
ತುಳು: ಕನಿಜೊ
Türkçe: Mineral
українська: Мінерал
اردو: معدن
Vahcuengh: Gvangvuz
Tiếng Việt: Khoáng vật
Võro: Mineraal
Winaray: Mineral
吴语: 礦物
ייִדיש: מינעראל
粵語: 礦物
中文: 礦物