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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 **S ...
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 when ...
. 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 Scratch or scratching may refer to: Science and technology * Scratch (programming language), an educational programming language developed by MIT Media Lab * Scratch space, space on the hard disk drive that is dedicated for only temporary stor ...
hardness comparison. 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 Vaterite is a mineral, a polymorph of calcium carbonate ( Ca C O3). It was named after the German mineralogist Heinrich Vater. It is also known as mu- calcium carbonate (μ-CaCO3). Vaterite belongs to the hexagonal crystal system, whereas cal ...
. 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. Chal ...
. When applied by
archaeologists Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural lands ...
and stone trade professionals, the term
alabaster Alabaster is a mineral or rock that is soft, often used for carving, and is processed for plaster powder. Archaeologists and the stone processing industry use the word differently from geologists. The former use it in a wider sense that includes ...
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 dryw ...
; but also for a similar-looking, translucent variety of fine-grained banded deposit of calcite.

# Unit cell and Miller indices

In publications, two different sets of Miller indices 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 In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessari ...
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 In geometry, a rhombohedron (also called a rhombic hexahedron or, inaccurately, a rhomboid) is a three-dimensional figure with six faces which are rhombi. It is a special case of a parallelepiped where all edges are the same length. It can be ...
, having approximate dimensions and , while the structural unit cell is
hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") or sexagon (from Latin , meaning "six") is a six-sided polygon or 6-gon creating the outline of a cube. The total of the internal angles of any simple (non- ...
(i.e. a rhombic
prism Prism usually refers to: * Prism (optics), a transparent optical component with flat surfaces that refract light * Prism (geometry) In geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics Mathemati ...
), 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 t ...
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 densest ...
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 forms. 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 sedimentary ...
, 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 sli ...
, but difficult to obtain. Scalenohedral faces are
chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from ...
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 flu ...
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, th ...
. A transparent variety called " Iceland spar" is used for optical purposes. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the
rhombohedral In geometry, a rhombohedron (also called a rhombic hexahedron or, inaccurately, a rhomboid) is a three-dimensional figure with six faces which are rhombi. It is a special case of a parallelepiped where all edges are the same length. It can be ...
form is sometimes referred to as "nailhead spar". The rhombohedral form may also have been the " sunstone" whose use by Viking navigators is mentioned in the Icelandic Sagas. Single calcite crystals display an optical property called birefringence (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
precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
d by groundwater, depending on such factors as the water temperature, pH, and dissolved
ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conv ...
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 c ...
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-resist ...
. 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 ta ...
. 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 uninc ...
, . Calcite can also contain small quantities of iron and
manganese Manganese is a chemical element with the 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 industrial alloy ...
. 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 Alabaster is a mineral or rock that is soft, often used for carving, and is processed for plaster powder. Archaeologists and the stone processing industry use the word differently from geologists. The former use it in a wider sense that includes ...
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 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 prism A Nicol prism is a type of polarizer, an optical device made from calcite crystal used to produce and analyse plane polarized light. It is made in such a way that it eliminates one of the rays by total internal reflection, i.e. the ordinary r ...
s) prior to the invention of Polaroid 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 Carrara marble, Luna marble to the Romans, is a type of white or blue-grey marble popular for use in sculpture and building decor. It has been quarried since Roman times in the mountains just outside the city of Carrara in the province of Mas ...
, 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 particl ...
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 Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, cau ...
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 metamorphos ...
. 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 cir ...
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 a ...
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 typically c ...
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
carbonatite Carbonatite () is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geochemical verification. Carbonati ...
s,
kimberlite Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of ...
s, 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 cr ...
(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 commonl ...
), 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 ...
, 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 through ...
s,
brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...
s,
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 se ...
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 Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...
(such as oysters 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 organisms ...
). Calcite is found in spectacular form in the Snowy River Cave of
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Kere ...
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 Bancroft () is a town located on the York River in Hastings County in the Canadian province of Ontario. It was first settled in the 1850s by United Empire Loyalists and Irish immigrants. From the mid-1950s to about 1982, mining was the prima ...
.
Bedding Bedding, also known as bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environ ...
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 Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and ...
during
diagenesis Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play ...
.

# 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 (ACC) via an
Ostwald ripening Ostwald ripening is a phenomenon observed in solid solutions or liquid sols that describes the change of an inhomogeneous structure over time, i.e., small crystals or sol particles dissolve, and redeposit onto larger crystals or sol particles ...
process, or via the agglomeration of
nanocrystal A ''nanocrystal'' is a material particle having at least one dimension smaller than 100 nanometres, based on quantum dots (a nanoparticle) and composed of atoms in either a single- or poly-crystalline arrangement. The size of nanocrystals dis ...
s. The crystallization of ACC can occur in two stages. First, the ACC nanoparticles rapidly dehydrate and crystallize to form individual particles of
vaterite Vaterite is a mineral, a polymorph of calcium carbonate ( Ca C O3). It was named after the German mineralogist Heinrich Vater. It is also known as mu- calcium carbonate (μ-CaCO3). Vaterite belongs to the hexagonal crystal system, whereas cal ...
. Second, the vaterite transforms to calcite via a dissolution and Precipitation (chemistry), reprecipitation mechanism, with the reaction rate controlled by the surface area 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 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 ta ...
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 Base (chemistry), basic initial pH, the transformation to calcite occurs via Metastability, 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 activity, such as sulfate-dependent anaerobic oxidation of methane, where methane is Redox, oxidized and sulfate is Redox, reduced, leading to precipitation of calcite and pyrite from the produced bicarbonate and sulfide. These processes can be traced by the specific carbon isotope composition of the calcites, which are extremely depleted in the Carbon-13, 13C isotope, by as much as −125 per mil Δ13C#Reference standard, PDB (δ13C).

# In Earth history

Calcite seas existed in Earth's history when the primary inorganic Precipitation (chemistry), 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 seas over the Phanerozoic, being most prominent in the Ordovician and Jurassic periods. Lineages evolved to use whichever Polymorphism (materials science), 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. Petrography, 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 catalysis, catalyze an important biological reaction, the formose reaction, and may have had a role in the origin of life. Interaction of its Chirality, chiral surfaces (see #Form, Form) with aspartic acid 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 (biology), test of the Cystoidea, cystoid ''Echinosphaerites, Echinosphaerites aurantium'' (Middle Ordovician, northeastern Estonia) File:Calcite-Dolomite-Gypsum-159389.jpg, Rhombohedrons of calcite that appear almost as books of petals, piled up 3-dimensionally on the Matrix (geology), matrix 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 shell in a Folk classification#Folk's carbonate classification, biopelsparite File:OoidSurface01.jpg, Grainstone with calcite ooids and Spar (mineralogy), sparry calcite cement; Carmel Formation, Middle Jurassic, of southern Utah, USA. File:Calcite-Aragonite-Sulphur-69380.jpg, Several well formed milky white casts, made up of many small sharp calcite crystals, from the sulfur mines at Agrigento, Sicily File:Calcite-tch21c.jpg, Reddish rhombohedral calcite crystals from China. Its red color is due to the presence of iron File:Calcite-75480.jpg, Cobaltoan, the cobalt-rich variety of calcite File:Calcite-114508.jpg, Sand calcites (calcites heavily included with desert sand) in South Dakota, USA File:RM463c-calcite-butterfly-twin.jpg, Calcite, butterfly twin, . José María Patoni, San Juan del Río, Durango (Mexico)