In contrast to rock, a mineral (from Mittellat. Aes minerale "pit ore", coined in the 16th century according to the French model) is a single element or a single chemical compound , which is generally crystalline and formed by geological processes. The plural is minerals (used in science in Germany and Austria) or minerals (used by collectors, dealers and in German-speaking Switzerland as a synonym for minerals).
The majority of the around 5,600 mineral species known today and recognized as independently by the International Mineralogical Association (IMA) (as of 2020) are inorganic , but some organic substances such as mellite and evenkite or the kidney stone formers whewellite and weddellite are also recognized as minerals because they can also be formed in the wild. Including all known mineral varieties and synonymous names (approx. 1200) as well as not yet recognized mineral types (approx. 120), there are over 6,800 mineral names (as of 2018/19).
Delimitations and exceptions
The terms “chemical element” and “chemical compound” contain a fixed composition and a defined chemical structure . Mixtures of substances are not minerals. However, the compositions of minerals can show some variation ( mixed crystals ) as long as they are structurally homogeneous.
A chemical compound can occur with different structures. Chemically uniform mixtures of different phases with different structures are also not minerals. So z. B. flint (chert) consist of pure SiO 2 , but is not a mineral, but a mixture of the structurally different minerals deep quartz , mogánite and opal and thus a rock .
Some naturally occurring compounds are not crystalline. These substances can be divided into two categories:
- amorphous: these are substances that were never crystalline.
- metamict: Formerly crystalline substances whose long-range order has been destroyed by ionizing radiation .
The determination of structure and composition with a completeness sufficient to clearly distinguish amorphous phases from one another is usually difficult or even impossible. Therefore, non-crystalline natural compounds are summarized by many scientists under the name mineraloids . However, the term is mainly used in American textbooks. In contrast, it has not been introduced in the German-speaking area.
Natural, amorphous substances can be recognized as minerals if the following conditions are met:
- Complete chemical analyzes covering the entire composition range of the substance
- Physicochemical (spectroscopic) data that prove the uniqueness of the substance
- The substance cannot be converted into a crystalline state by physical treatment (e.g. heating).
Metamorphosed substances can be minerals if it can be proven that the substance was originally crystalline and had the same composition (e.g. fergusonite-Y ).
Liquids are generally not counted among the minerals. For example, liquid water is not a mineral, but ice is. An exception is mercury : As an element on earth, it only occurs in liquid and gaseous form, but as a liquid is still recognized as a mineral. Crude oil and all other bitumen , including solid, non-crystalline bitumen, are mixtures of substances and not minerals.
The processes that lead to the formation of extraterrestrial substances, e.g. B. in meteorites and lunar rocks , are similar to those that also take place on earth. As a result, naturally occurring components of extraterrestrial stones and cosmic dust are called minerals (e.g. tranquilityite , Brownleeit ).
Man-made substances are not minerals. When such anthropogenic substances are identical to minerals, they are referred to as "synthetic equivalents".
Materials that have been created from synthetic substances through geological processes are not generally referred to as minerals. Exceptions are some substances that were previously recognized as minerals, e.g. B. some minerals that were formed by the reaction of ancient metallurgical slag with sea water.
Natural substances that have been converted by human activities can be recognized as minerals if the human activities were not directed directly towards the creation of new substances. Substances that are newly formed in pit or dump fires can be recognized by the IMA if the fire was not triggered by humans and no material of anthropic origin was deposited there.
Biogenic substances are compounds that have been formed exclusively through biological processes without a geological component, such as B. mussel shells or oxalate crystals in plant tissues. These compounds are not minerals.
Once geological processes have been involved in the formation of the compounds, these substances can be recognized as minerals. Examples of this are minerals that have formed from organic components in black slate or from bat guano in caves, as well as components of limestone or phosphorites of organic origin.
With the exception of natural glasses and coal rocks , all rocks on earth and other celestial bodies are made up of minerals. The most common are around thirty minerals, the so-called rock formers . In addition, minerals are also found as colloids in water or as fine dust in the air. Water itself is also a mineral when it is in the form of water ice .
Minerals are formed
- through crystallization from melts ( igneous mineral formation) or from aqueous solutions ( hydrothermal and sedimentary mineral formation) or from gases through resublimation ( e.g. on volcanoes )
- during metamorphosis through solid-state reactions from other minerals or natural glasses.
Primary minerals arise at the same time as the rock of which they are a part, while secondary minerals are formed as a result of subsequent changes in the rock (metamorphosis, hydrothermal overprinting or weathering ).
A distinction is made between two phases of mineral formation: First, several atoms or ions accumulate and form a crystallization nucleus ( nucleation ). If this exceeds a critical nucleus radius, it continues to grow and a mineral develops ( crystal growth ). After numerous transformation reactions with other minerals, with the air or with the water , the minerals are finally destroyed by weathering. The ions from which the crystal lattice was built go back into solution or, in anatexis, end up in a rock melt ( magma ). Eventually the cycle will start over in a different place.
To determine the cooling point, see cracks .
A special form of mineral formation from the solution is biomineralization . This means the formation of minerals by organisms. The following minerals can arise in this way:
- Calcite , vaterite and aragonite form the shells of snails , mussels , foraminifera and coccolithophores .
- Hydroxyapatite builds the bones of all vertebrates and together with fluoroapatite builds the tooth enamel of mammals .
- Magnetite is used by a number of living things as a compass for orientation in the earth's magnetic field . This was first found in magnetotactic bacteria. It is also known today from insects , mollusks , fish , birds and mammals.
Other forms of mineral formation from solution or through the reaction of minerals with water play a role in technical mineralogy :
Calcite is used to neutralize acids, including carbon dioxide, with the formation of water hardness , pyrite acts as a reducing agent in the bacterial elimination of nitrate through denitrification , while clay minerals can cause neutralization reactions at low pH values and ion exchange reactions. When treating drinking water , the reaction products of the elimination of iron (II) and manganese ions are goethite and δ-MnO 2 , calcite can be formed during softening reactions (decarbonisation). In wastewater treatment, clear crystals of struvite , an ammonium magnesium phosphate, can form if the phosphate concentrations in the wastewater treatment plants are sufficiently high . These can narrow the cross-section of lines. In the event of corrosion of steel and cast iron in contact with water, depending on the nature of the water, goethite, magnetite and lepidocrocite , with higher carbonate hardness also siderite , in phosphate -containing waters vivianite , in sulphate-containing waters troilit and in water containing hydrogen sulphide greigit can be formed. Cuprite , malachite or azurite can be formed from copper , while lead mainly forms hydrocerussite .
Outwardly, freely crystallized minerals show a geometric shape with defined natural surfaces that are in fixed angular relationships to one another, depending on the specific crystal system to which the mineral is assigned. This is also known as the law of angular constancy ( Nicolaus Steno ). The symmetrical arrangement of the surfaces is an expression of the inner structure of a crystalline mineral: It shows a well-ordered atomic structure, which is created by repeatedly lining up so-called unit cells , which make up the smallest structural unit of the mineral. Due to the internal symmetry, a distinction is made between six to seven crystal systems , namely the cubic, the hexagonal, the trigonal, the tetragonal, the orthorhombic, the monoclinic and the triclinic system. The hexagonal and the trigonal systems are occasionally combined by some mineralogists. Two or more mineral individuals that have grown together in a certain crystallographic orientation are called twins . They arise when the rock grows or deforms. Multiple twins often form what are known as twin lamellae, which must not be confused with the segregation lamellae that arise when a mixed crystal becomes thermodynamically unstable during cooling and precipitates form.
Determination with the naked eye:
Color : A distinction is made between idiochromatic minerals (for example cinnabarite ), which are colored by the active formula elements , allochromatic minerals (for example quartz ), whose different colors often result from various trace elements and defects in the crystal lattice, and pseudochromatic minerals, whose colors are like opals caused by refraction or interference.
In ore microscopy you can always see the complementary color of the real color, since the incident light is used.
- The color in minerals results from the absorption of light of the complementary color through one or more of the following processes:
- Transitions of electrons between the d or f orbitals of the transition metals or lanthanoids split by the crystal field (e.g. the red color of the ruby due to chromium ions on the aluminum position )
- Transitions of electrons between two cations or between cation and anion (e.g. the blue color of sapphire due to transitions between titanium and iron impurities )
- Transitions of electrons from the valence band to the conduction band of semiconductors (e.g. the red color of the cinnabarite)
- Transitions of electrons from the valence band to the acceptor level of an impurity (e.g. blue coloration of diamond due to boron )
- Transitions of electrons from the donor level of an impurity to the conduction band (e.g. yellow coloration of diamond due to nitrogen )
- Transitions of electrons between s and d bands in conductors (e.g. color of gold )
- Change of the energy state of an electron on an anion vacancy
- Diffraction effects on low-dimensional structures (e.g. opal )
- Stroke color : It is the color of the powdered mineral, which is often different from the color of its surface. In the case of silicates , the line is lighter than its own color; in the case of sulfides , it is darker. If a mineral can have several colors, the line color is usually white (e.g. corundum, beryl), as is the case with colorless minerals. If a mineral can only have one color, this often corresponds to the color of the line (e.g. lazurite, malachite). The line is usually tested on an unglazed ceramic plate.
- Gloss : A distinction is made between matt (i.e. the mineral shows no gloss at all), silk gloss (like a shimmer of light on natural silk), mother-of-pearl gloss (like the inside of some seashells), glass gloss (like simple window glass), greasy gloss (like fat), diamond gloss (like a cut diamond), metallic luster (like polished metal) and wax luster.
- Transparency : A distinction is made between transparent (e.g. calcite), translucent ( e.g. hematite ) and opaque minerals ( e.g. cassiterite ). As a rule, rock-forming minerals are transparent or translucent and ores are opaque. Therefore, the former are examined in transmitted light and the latter in reflected light.
- Crystal form : The crystal form is made up of the costume and the habitus . The former denotes the dominant crystallographic shape , the latter the ratio of the lengths of the crystal.
Determination with polarization microscopy in transmitted light:
- Pleochroism : With some transparent minerals, the colors and depths of color are different in different directions. If two colors appear, this is called dichroism , if three colors appear, trichroism or pleochroism. The term is also used as a collective term for both types of multicolor.
- Refractive index : The ratio of the speed of light in air to the speed of light in the mineral is determined by immersion methods , approximately also by the strength of the relief and the movement of Becke's line, a light line on a grain boundary , when moving the microscope stage. The following applies: Down (with the table), higher (mineral with the higher refraction of light than the neighboring mineral ), in (movement of Becke's line).
- Birefringence : difference in the refractive indices in the different directions of the crystal. It is determined from the interference color under crossed polarizers with the help of color tables .
Determination with polarization microscopy in incident light (ore microscopy):
- Reflectance : proportion of the reflected light. Determination by means of ore microscopy. Characteristic for distinguishing gold from sulphide minerals.
- Bireflectance : Directional dependence of the color in ore microscopy, which can be seen under a polarizer.
- Anisotropy effects : color phenomena in opaque minerals that can be observed under crossed polarizers in ore microscopy.
- Internal reflections : Diffuse reflection of the light at the interfaces with impurities, which corresponds to the line color and is best visible under crossed polarizers in the dark position.
Determination with special microscopes:
- Luminescence : Some minerals emit light when they experience some kind of stimulation. Depending on the type of excitation, a distinction is made among other things chemiluminescence , triboluminescence , cathodoluminescence and thermoluminescence , and according to the type of light emitted, UV, VIS and IR luminescence. Short luminescence means fluorescence , longer lasting phosphorescence .
- Density : It depends on the chemical composition and structure. The density of the minerals, rocks and ores varies between 1 and 20 ( g · cm −3 ). Values below 2 are perceived as light (amber 1.0), those from 2 to 4 as normal (quartz 2.6) and those above 4 appear to us as heavy (galena 7.5). Minerals with a density of> 3.0 are called heavy minerals . The density separation is an important treatment method. If the density is related to the density of water, it is called the relative density "o" and is then without a unit.
- Hardness : It is determined by the stability of the chemical bonds in the mineral and determined by their scratch resistance. It is indicated in mineralogy by its value on the Mohs scale, which ranges from 1 (very soft, e.g. talc ) to 10 (very hard, e.g. diamond).
- Cleavage : The tendency of a mineral to split along certain crystallographic planes. A distinction is made between non-existent cleavage (for example quartz), indistinct cleavage (for example beryl ), clear cleavage (for example apatite ), good cleavability (for example diopside ), perfect cleavage (for example sphalerite ) and extremely perfect cleavage (for example mica ). It describes crystal planes between which only weak forces exist and at which the crystal can therefore be split. For example, calcite has three cleavage planes and is therefore very completely fissile. In contrast, quartz has no cleavage plane at all.
- Fracture behavior : If a mineral does not break along its cleavage planes, characteristic fracture structures often occur. A distinction is made between shell-like breakage (for example quartz), fibrous breakage (for example kyanite ), splintery breakage (for example chrysotile ), flat breakage and uneven breakage.
- Toughness or tenacity : A distinction is made between brittle minerals (for example quartz) and flexible ones (for example muscovite ).
- Magnetism : A distinction is made between ferromagnetic minerals ( e.g. iron), ferrimagnetic minerals (e.g. magnetite), paramagnetic minerals ( e.g. biotite ), diamagnetic minerals (e.g. quartz) and antiferromagnetic minerals (e.g. hematite). Usually only ferro- and ferrimagnetism are determined with the help of a compass needle .
- Electrical conductivity : Most minerals are non-conductors, some sulfides and oxides are semiconductors , and solid metals are conductors . Covellin is the only known naturally occurring mineral superconductor with a transition temperature of 1.63 Kelvin .
- Piezoelectricity : Ability to convert a mechanical vibration into an electrical alternating voltage and vice versa. Example: quartz.
- Pyroelectricity : Ability to convert a temperature difference into charge separation. Example: tourmaline
- Flame color : some elements color a flame. This property is used in the flame test to infer the chemical composition of a mineral. Gas burners are best suited for this in darkened rooms.
- Meltability : It describes the behavior in front of the soldering tube , i.e. the melting reaction.
- Reaction with hydrochloric acid : Carbonates react differently with hot and sometimes with cold hydrochloric acid. This property is an important diagnostic criterion for this mineral group .
Sulfur-containing minerals can often be recognized by the smell that arises when they are hit.
- Radioactivity : This is the property of emitting high-energy radiation without adding any energy. There are traditionally three types of rays: alpha, beta and gamma rays. The radiation measurement is carried out with a Geiger counter . Radioactivity is potentially harmful to health even in low doses. Radioactive minerals are, for example, uraninite , but also apatite, which incorporates uranium as a trace element instead of phosphorus .
- Mobilization : Minerals are mobilized through mining , but can also be released through natural processes ( erosion ). In the case of the toxicologically relevant minerals containing heavy metals , the mobilization by humans far exceeds the natural processes.
Every mineral is thermodynamically stable only under certain pressure - temperature conditions. Outside of its stability range, it changes over time into the stable modification there . Some phase changes occur suddenly when leaving the stability field (for example high quartz - low quartz ), others are kinetically inhibited and last millions of years. In some cases the activation energy is so high that the thermodynamically unstable modification is retained as a metastable phase (for example diamond- graphite ). This inhibition of the reaction leads to a “freezing” of the thermodynamic equilibrium that prevailed at an earlier point in time. Therefore, the mineral inventory of a rock provides information about the formation and development history of a rock and thus contributes to the knowledge of the origin and development of planet earth (see also Presolar Mineral ).
Mineral raw materials are divided into energy raw materials , property raw materials and element raw materials . Energy resources are for example the minerals uraninite and thorite as nuclear fuels . Property raw materials are used in technology without chemical decomposition, including, for example, quartz for glass and clay minerals for the ceramic industry. Elemental raw materials are mined with the aim of extracting a specific chemical element. If it is a metal, one speaks of an ore. An enrichment of raw materials is called a deposit if it is economically minable. The term is therefore economic, not scientific: Whether a given deposit can be commercially exploited depends on the mining and processing costs and the market value of the metal it contains - while the iron content of minerals must be up to 50% to be financially In 2003, a share of 0.00001% of the much more valuable platinum was enough to achieve a profit . In addition to the classification according to the use of the raw material, a classification according to the origin is also common. Sedimentary deposits, such as the banded iron ore formations, were formed through precipitation reactions when the pH value, pressure and temperature changed or through the influence of bacteria or through weathering processes and the transport of minerals from their original area of origin and their deposition as ( soaps ), for example from soap gold , at the bottom of rivers, lakes or shallow seas. Hydrothermal reservoirs are formed when surface or deep water dissolves certain elements from the surrounding rocks and deposits them elsewhere or from residual fluids after the solidification of a magma. Igneous deposits result from the crystallization of a magma. One example are many platinum and chromite deposits. Metamorphic deposits only arise through the transformation of rocks, for example marble deposits .
Some minerals are used as jewelry . If they are transparent and their hardness is greater than 7, they are called gemstones , otherwise they are called gemstones . 95 percent of global sales in this market are achieved with diamonds, the rest almost predominantly with sapphires, emeralds , rubies and tourmalines. In order to bring out the beauty of a gemstone, which is influenced by color and luster, it must be cut and polished. There are numerous different cut forms for this purpose: Transparent or translucent varieties are usually provided with facet cuts, in which surfaces that are usually in fixed angular relationships to one another, the so-called facets, maximize the light reflection. Opaque minerals, on the other hand, receive smooth, single-surface cuts. The asterism effect of a star sapphire, for example, can only be achieved with the cabochon cut . The fire of a brilliant cut diamond depends mainly on the observance of certain angular relationships of the individual facets and is created by the splitting of the white light into the individual visible colors ( dispersion ).
Some minerals are also used as body care products, such as the clay mineral lava earth , which has been used as body and hair cleaning products since ancient times . Other minerals, such as talc , serve as raw materials in the fine arts as well as medicinal purposes ( pleurodesis , lubricants in tablet production).
In many ancient cultures, but also in modern esotericism , certain minerals are said to have certain protective and healing effects . For example, was already in ancient Egypt of carnelian because of its color reminiscent of blood as the "Stone of Life" and played at funeral rituals as well as protective and Gem of the Pharaohs a corresponding role. The alleged healing and protective powers of amber , which were already described by Thales von Milet and Hildegard von Bingen , are also legendary .
Minerals can also be important as collectibles , either in scientific mineral collections to represent the mineral inventory of a site (type material) or for private hobby collectors who have specialized in site collections or various systematic collections. Due to the rarity of many minerals, which are often only available in very small samples, private collectors specializing in systematic collections also like to collect micromounts for reasons of space and costs .
Systematics of the minerals
- EH Nickel: The Definition of a Mineral . In: The Canadian Mineralogist . tape 33 , 1995, pp. 689–690 ( mineralogicalassociation.ca [PDF; 270 kB ; accessed on June 25, 2020]).
- Ernest H. Nickel, Joel D. Grice: The IMA Commission on new Minerals and Mineral Names: Procedures and Guidelines on Mineral Nomenclature . In: The Canadian Mineralogist . tape 36 , 1998, pp. 1–16 (English, cnmnc.main.jp [PDF; 316 kB ; accessed on June 25, 2020]).
- Josef Ladurner, Fridolin Purtscheller: The great mineral book . 2nd, revised edition. Pinguin Verlag, Innsbruck 1970 ( available online at austria-forum.org ).
- Dietlinde Goltz: Studies on the history of mineral names in pharmacy, chemistry and medicine from the beginnings to Paracelsus. (Mathematical and natural science dissertation, Marburg an der Lahn 1966) Wiesbaden 1972 (= Sudhoffs Archive , Supplement 14).
- William A. Deer, Robert A. Howie, Jack Zussman: Orthosilicates (= Rock-Forming Minerals . No. 1 ). 2nd Edition. Longman, London 1982, ISBN 0-582-46526-5 .
- Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 .
- Petr Korbel, Milan Novák: Mineral Encyclopedia (= Villager Nature ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 .
- Andreas Landmann: Gemstones and Minerals . 25th edition. Franconian Crumbach, 2004, ISBN 3-89736-705-X .
- Will Kleber , Hans-Joachim Bautsch , Joachim Bohm , Detlef Klimm: Introduction to crystallography . 19th edition. Oldenbourg Wissenschaftsverlag, 2010, ISBN 978-3-486-59075-3 .
- Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
- Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 .
- Homepage of the International Mineralogical Association - Commission on New Minerals, Nomenclature and Classification (CNMNC). In: cnmnc.main.jp. International Mineralogical Association , accessed June 25, 2020 .
- Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: March 2020. (PDF; 2.44 MB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2020, accessed June 25, 2020 .
- Christoph Lenz: The difficulty of defining the term mineral. In: geoberg.de. from February 3, 2005 ( Memento from October 16, 2013 in the Internet Archive )
- Mineralienatlas main page , Mineralienatlas: Mineral (Wiki and database, German)
- Mindat.org. Hudson Institute of Mineralogy, accessed on June 25, 2020 (English, extensive mineral, picture and reference database).
- The Definition of a Mineral, Nickel 1995
- Duden: Mineral .
- Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: July 2020. (PDF; 3.07 MB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, July 2020, accessed July 19, 2020 .
- Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
- Martin Okrusch, Siegfried Matthes: Mineralogie. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 4 .
- Ritsuro Miyakaki, Frédéric Hatert, Marco Pasero, Stuart J. Mills: IMA Commission on New Minerals, Nomenclature and Classification (CNMNC). Newsletter 50 . In: European Journal of Mineralogy . tape 31 , 2019, pp. 847–853 (English, cnmnc.main.jp [PDF; 303 kB ; accessed on April 13, 2020]).
- See e.g. B. Systematics of Minerals , 4.AA.05 .
- Francesco Di Benedetto and a .: First evidence of natural superconductivity: Covellite. In: European Journal of Mineralogy. 18, No. 3, 2006, pp. 283-287, doi: 10.1127 / 0935-1221 / 2006 / 0018-0283 .
- G. Eisenbrand, M. Metzler: Toxikologie für Chemiker , Georg Thieme Verlag, Stuttgart, New York 1994, p. 264, ISBN 3-13-127001-2 .