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Calcite is a
carbonate mineral Carbonate minerals are those minerals containing the carbonate ion, . Carbonate divisions Anhydrous carbonates *Calcite group: trigonal ** Calcite CaCO3 ** Gaspéite (Ni,Mg,Fe2+)CO3 ** Magnesite MgCO3 **Otavite CdCO3 ** Rhodochrosite MnCO3 ...
and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
. Calcite defines hardness 3 on the
Mohs scale of mineral hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by t ...
, based on scratch
hardness comparison A variety of hardness-testing methods are available, including the Vickers, Brinell, Rockwell, Meyer and Leeb tests. Although it is impossible in many cases to give an exact conversion, it is possible to give an approximate material-specific co ...
. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, and vaterite is even less stable.


Etymology

Calcite is derived from the German ''Calcit'', a term from the 19th century that came from the Latin word for lime, ''calx'' (genitive calcis) with the suffix "-ite" used to name minerals. It is thus etymologically related to
chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. C ...
. When applied by archaeologists and stone trade professionals, the term alabaster is used not just as in geology and mineralogy, where it is reserved for a variety of
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...
; but also for a similar-looking,
translucent In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions ...
variety of fine-grained banded deposit of calcite.


Unit cell and Miller indices

In publications, two different sets of
Miller indices Miller indices form a notation system in crystallography for lattice planes in crystal (Bravais) lattices. In particular, a family of lattice planes of a given (direct) Bravais lattice is determined by three integers ''h'', ''k'', and ''� ...
are used to describe directions in hexagonal and rhombohedral crystals, including calcite crystals: three Miller indices in the a_1, a_2, c directions, or four Bravais-Miller indices in the a_1,a_2,a_3,c directions, where i is redundant but useful in visualizing permutation symmetries. To add to the complications, there are also two definitions of unit cell for calcite. One, an older "morphological" unit cell, was inferred by measuring angles between faces of crystals, typically with a
goniometer A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. The term goniometry derives from two Greek words, γωνία (''gōnía'') 'angle' and μέτρον (''métron'') ' m ...
, and looking for the smallest numbers that fit. Later, a "structural" unit cell was determined using
X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. The morphological unit cell is rhombohedral, having approximate dimensions and , while the structural unit cell is
hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...
(i.e. a rhombic prism), having approximate dimensions and . For the same orientation, must be multiplied by 4 to convert from morphological to structural units. As an example, calcite cleavage is given as "perfect on " in morphological coordinates and "perfect on " in structural units. In \ indices, these are and , respectively. Twinning, cleavage and crystal forms are often given in morphological units.


Properties

The diagnostic properties of calcite include a defining
Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by ...
of 3, a
specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its dens ...
of 2.71 and, in crystalline varieties, a vitreous luster. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities.


Crystal habits

Calcite has numerous habits, representing combinations of over 1000
crystallographic form A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s. Most common are scalenohedra, with faces in the hexagonal directions (morphological unit cell) or directions (structural unit cell); and rhombohedral, with faces in the or directions (the most common cleavage plane). Habits include acute to obtuse rhombohedra, tabular habits,
prisms Prism usually refers to: * Prism (optics), a transparent optical component with flat surfaces that refract light * Prism (geometry), a kind of polyhedron Prism may also refer to: Science and mathematics * Prism (geology), a type of sedimentar ...
, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed habits. It may occur as fibrous, granular, lamellar, or compact. A fibrous, efflorescent habit is known as ''lublinite''. Cleavage is usually in three directions parallel to the rhombohedron form. Its fracture is
conchoidal Conchoidal fracture describes the way that brittle materials break or fracture when they do not follow any natural planes of separation. Mindat.org defines conchoidal fracture as follows: "a fracture with smooth, curved surfaces, typically slig ...
, but difficult to obtain. Scalenohedral faces are chiral and come in pairs with mirror-image symmetry; their growth can be influenced by interaction with chiral biomolecules such as L- and D-
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s. Rhombohedral faces are not chiral.


Optical

Calcite is transparent to
opaque Opacity or opaque may refer to: * Impediments to (especially, visible) light: ** Opacities, absorption coefficients ** Opacity (optics), property or degree of blocking the transmission of light * Metaphors derived from literal optics: ** In lingui ...
and may occasionally show
phosphorescence Phosphorescence is a type of photoluminescence related to fluorescence. When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Unlike fluo ...
or
fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
. A transparent variety called " Iceland spar" is used for optical purposes. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the rhombohedral form is sometimes referred to as "nailhead spar". The rhombohedral form may also have been the " sunstone" whose use by
Viking Vikings ; non, víkingr is the modern name given to seafaring people originally from Scandinavia (present-day Denmark, Norway and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded and se ...
navigators is mentioned in the Icelandic Sagas. Single calcite crystals display an optical property called
birefringence Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefri ...
(double refraction). This strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect (using calcite) was first described by the Danish scientist Rasmus Bartholin in 1669. At a wavelength of about 590 nm, calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the ordinary refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4.


Chemical

Calcite, like most carbonates, will dissolve in acids via the reaction :: The carbon dioxide released by this reaction produces a characteristic effervescence when dilute hydrochloric acid is dropped on a calcite sample. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite. The overall reaction is :: If the amount of dissolved carbon dioxide drops, the reaction reverses to precipitate calcite. As a result, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on such factors as the water temperature, pH, and dissolved ion concentrations. When conditions are right for precipitation, calcite forms mineral coatings that cement rock grains together and can fill fractures. When conditions are right for dissolution, the removal of calcite can dramatically increase the
porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
and permeability of the rock, and if it continues for a long period of time, may result in the formation of
cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
s. Continued dissolution of calcium carbonate-rich formations can lead to the expansion and eventual collapse of cave systems, resulting in various forms of
karst topography Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...
. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. Calcite is also more soluble at higher pressures. Pure calcite has the composition . However, the calcite in limestone often contains a few percent of
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
. Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from that of
dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...
, . Calcite can also contain small quantities of
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
and
manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...
. Manganese may be responsible for the fluorescence of impure calcite, as may traces of organic compounds.


Use and applications

Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast, whose name contributed to the term alabaster because of the close association. Many other cultures have used the material for similar carved objects and applications. A transparent variety of calcite known as Iceland spar may have been used by
Vikings Vikings ; non, víkingr is the modern name given to seafaring people originally from Scandinavia (present-day Denmark, Norway and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded and se ...
for navigating on cloudy days. High-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry. It was used as a polarizer (in Nicol prisms) prior to the invention of
Polaroid Polaroid may refer to: * Polaroid Corporation, an American company known for its instant film and cameras * Polaroid camera, a brand of instant camera formerly produced by Polaroid Corporation * Polaroid film, instant film, and photographs * Polar ...
plates and still finds use in optical instruments. Also, experiments have been conducted to use calcite for a cloak of invisibility. Microbiologically precipitated calcite has a wide range of applications, such as soil remediation, soil stabilization and concrete repair. Calcite, obtained from an 80 kg sample of Carrara marble, is used as the
IAEA The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was established in 195 ...
-603 isotopic standard in
mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is u ...
for the calibration of δ18O and δ13C.


Natural occurrence

Calcite is a common constituent of
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
s, limestone in particular, much of which is formed from the shells of dead marine organisms. Approximately 10% of sedimentary rock is limestone. It is the primary mineral in metamorphic
marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorphose ...
. It also occurs in deposits from
hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...
s as a
vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...
mineral; in caverns as
stalactite A stalactite (, ; from the Greek 'stalaktos' ('dripping') via ''stalassein'' ('to drip') is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble ...
s and
stalagmite A stalagmite (, ; from the Greek , from , "dropping, trickling") is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typicall ...
s; and in
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...
or mantle-derived rocks such as carbonatites, kimberlites, or rarely in
peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high pr ...
s. Calcite is often the primary constituent of the shells of marine organisms, such as
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...
(such as
coccolith Coccoliths are individual plates or scales of calcium carbonate formed by coccolithophores (single-celled phytoplankton such as '' Emiliania huxleyi'') and cover the cell surface arranged in the form of a spherical shell, called a ''coccosphere' ...
s and planktic
foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...
), the hard parts of red
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
, some
sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throu ...
s, brachiopods,
echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the ...
s, some serpulids, most
bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...
, and parts of the shells of some bivalves (such as
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...
s and
rudists Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organis ...
). Calcite is found in spectacular form in the
Snowy River Cave Snowy River Cave Passage is a cave passage within Fort Stanton Cave in Lincoln County, New Mexico, obtaining its name from a stream bed of white calcite. Geology The bed of Snowy River is covered with bright white calcite. Over time, ancient, s ...
of
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...
as mentioned above, where microorganisms are credited with natural formations.
Trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...
s, which became extinct a quarter billion years ago, had unique compound eyes that used clear calcite crystals to form the lenses. It also forms a substantial part of birds' eggshells, and the δC of the diet is reflected in the δC of the calcite of the shell. The largest documented single crystal of calcite originated from Iceland, measured and and weighed about 250 tons. Classic samples have been produced at Madawaska Mine, near Bancroft, Ontario. Bedding parallel veins of fibrous calcite, often referred to in quarrying parlance as ''beef'', occur in dark organic rich mudstones and shales, these veins are formed by increasing fluid pressure during diagenesis.


Formation processes

Calcite formation can proceed by several pathways, from the classical
terrace ledge kink model In chemistry, the Terrace Ledge Kink model (TLK), which is also referred to as the Terrace Step Kink model (TSK), describes the thermodynamics of crystal surface formation and transformation, as well as the energetics of surface defect formation. I ...
to the crystallization of poorly ordered precursor phases like
amorphous calcium carbonate Amorphous calcium carbonate (ACC) is the amorphous and least stable polymorph of calcium carbonate. ACC is extremely unstable under normal conditions and is found naturally in taxa as wide-ranging as sea urchins, corals, mollusks, and foraminifer ...
(ACC) via an Ostwald ripening process, or via the agglomeration of nanocrystals. The crystallization of ACC can occur in two stages. First, the ACC nanoparticles rapidly dehydrate and crystallize to form individual particles of vaterite. Second, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism, with the reaction rate controlled by the
surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ...
of a calcite crystal. The second stage of the reaction is approximately 10 times slower. However, crystallization of calcite has been observed to be dependent on the starting pH and
concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', ''number concentration'', ...
of
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
in solution. A neutral starting pH during mixing promotes the direct transformation of ACC into calcite without a vaterite intermediate. But when ACC forms in a solution with a basic initial pH, the transformation to calcite occurs via metastable vaterite, following the pathway outlined above. Magnesium has a noteworthy effect on both the stability of ACC and its transformation to crystalline CaCO3, resulting in the formation of calcite directly from ACC, as this ion destabilizes the structure of vaterite. Calcite may form in the subsurface in response to
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
activity, such as sulfate-dependent
anaerobic oxidation of methane Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
, where
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
is
oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
and sulfate is reduced, leading to precipitation of calcite and
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
from the produced
bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemi ...
and
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
. These processes can be traced by the specific carbon isotope composition of the calcites, which are extremely depleted in the 13C isotope, by as much as −125 per mil PDB13C).


In Earth history

Calcite sea A calcite sea is a sea in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. An aragonite sea is the alternate seawater chemistry in which aragonite and high-magnesium calcite are the primary inorganic ca ...
s existed in Earth's history when the primary inorganic precipitate of calcium carbonate in marine waters was low-magnesium calcite (lmc), as opposed to the aragonite and high-magnesium calcite (hmc) precipitated today. Calcite seas alternated with
aragonite sea An aragonite sea contains aragonite and high-magnesium calcite as the primary inorganic calcium carbonate precipitates. The chemical conditions of the seawater must be notably high in magnesium content relative to calcium (high Mg/Ca ratio) for ...
s over the Phanerozoic, being most prominent in the Ordovician and
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
periods. Lineages evolved to use whichever morph of calcium carbonate was favourable in the ocean at the time they became mineralised, and retained this mineralogy for the remainder of their evolutionary history. Petrographic evidence for these calcite sea conditions consists of calcitic ooids, lmc cements, hardgrounds, and rapid early seafloor aragonite dissolution. The evolution of marine organisms with calcium carbonate shells may have been affected by the calcite and aragonite sea cycle. Calcite is one of the minerals that has been shown to catalyze an important biological reaction, the
formose reaction The formose reaction, discovered by Aleksandr Butlerov in 1861, and hence also known as the Butlerov reaction, involves the formation of sugars from formaldehyde. The term formose is a portmanteau of formaldehyde and aldose. Reaction and mechanism ...
, and may have had a role in the origin of life. Interaction of its chiral surfaces (see
Form Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data * ...
) with
aspartic acid Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pro ...
molecules results in a slight bias in chirality; this is one possible mechanism for the origin of homochirality in living cells.


Gallery

File:Calcite-Mottramite-cktsu-45b.jpg, Calcite with mottramite File:Erbenochile eye.JPG,
Trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...
eyes employed calcite File:CalciteEchinosphaerites.jpg, Calcite crystals inside a
test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...
of the
cystoid Cystoidea is a class of extinct crinozoan echinoderms, termed cystoids, that lived attached to the sea floor by stalks. They existed during the Paleozoic Era, in the Middle Ordovician and Silurian Periods, until their extinction in the Devo ...
'' Echinosphaerites aurantium'' (Middle Ordovician, northeastern
Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, an ...
) File:Calcite-Dolomite-Gypsum-159389.jpg, Rhombohedrons of calcite that appear almost as books of petals, piled up 3-dimensionally on the
matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** '' The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchi ...
File:Calcite-Hematite-Chalcopyrite-176263.jpg, Calcite crystal canted at an angle, with little balls of hematite and crystals of chalcopyrite both on its surface and included just inside the surface of the crystal File:GeopetalCarboniferousNV.jpg, Thin section of calcite crystals inside a recrystallized
bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of marine and freshwater Mollusca, molluscs that have laterally compressed bodies enclosed by a shell consisting of two hing ...
shell in a biopelsparite File:OoidSurface01.jpg, Grainstone with calcite ooids and sparry calcite cement;
Carmel Formation The Carmel Formation is a geologic formation in the San Rafael Group that is spread across the U.S. states of Wyoming, Utah, Colorado, north east Arizona and New Mexico. Part of the Colorado Plateau, this formation was laid down in the Middle ...
, Middle
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
, of southern
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
, USA. File:Calcite-Aragonite-Sulphur-69380.jpg, Several well formed milky white casts, made up of many small sharp calcite crystals, from the
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
mines at
Agrigento Agrigento (; scn, Girgenti or ; grc, Ἀκράγας, translit=Akrágas; la, Agrigentum or ; ar, كركنت, Kirkant, or ''Jirjant'') is a city on the southern coast of Sicily, Italy and capital of the province of Agrigento. It was one o ...
,
Sicily (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...
File:Calcite-tch21c.jpg, Reddish rhombohedral calcite crystals from
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
. Its red color is due to the presence of
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
File:Calcite-75480.jpg,
Cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
oan, the cobalt-rich variety of calcite File:Calcite-114508.jpg, Sand calcites (calcites heavily included with desert sand) in
South Dakota South Dakota (; Sioux: , ) is a U.S. state in the North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota and Dakota Sioux Native American tribes, who comprise a large po ...
, USA File:RM463c-calcite-butterfly-twin.jpg, Calcite, butterfly twin, . José María Patoni, San Juan del Río, Durango (
Mexico Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...
)


See also

* Ikaite, CaCO3·6H2O *
List of minerals This is a list of minerals for which there are articles on Wikipedia. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various ''species''. Within a m ...
*
Lysocline The lysocline is the depth in the ocean dependent upon the carbonate compensation depth (CCD), usually around 3.5 km, below which the rate of dissolution of calcite increases dramatically because of a pressure effect. While the lysocline is the u ...
*
Manganoan calcite Manganoan calcite or manganocalcite is a variety of calcite rich in manganese, which gives the mineral a pink color.Mang ...
, (Ca,Mn)CO3 * Monohydrocalcite, CaCO3·H2O *
Ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
* Ulexite


References


Further reading

* {{Authority control Calcium minerals Carbonate minerals Limestone Optical materials Transparent materials Calcite group Cave minerals Trigonal minerals Minerals in space group 167 Evaporite Luminescent minerals Polymorphism (materials science)