Calcite
Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico.
General
Category	Carbonate mineral
Chemical formula	CaCO3
Identification
Color	Colorless or white, also gray, yellow, green,
Crystal habit	Crystalline, granular, stalactitic, concretionary, massive. Carbonate minerals are those Minerals containing the Carbonate Ion: CO32- A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes In Mineralogy, shape and size give rise to descriptive terms applied to the typical appearance or habit of Crystals The many terms used by mineralogists
Crystal system	Trigonal Hexagonal Scalenohedral
Twinning	Common by four twin laws
Cleavage	Perfect on [1011], [1011] and [1011]
Fracture	Brittle - conchoidal
Mohs Scale hardness	3
Luster	Vitreous
Refractive index	nω = 1. A crystal system is a category of Space groups which characterize Symmetry of structures in three dimensions with Translational symmetry in three directions In Crystallography, the rhombohedral (or trigonal) Crystal system is one of the seven lattice point groups named after the two-dimensional Crystal twinning occurs when two separate crystals share some of the same Crystal lattice points in a symmetrical manner Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types In the field of Mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a Mineral is broken The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material Lustre (or luster) is a description of the way light interacts with the surface of a Crystal, rock, or Mineral. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 640 - 1. 660 nε = 1. 486
Optical Properties	Uniaxial (-)
Birefringence	δ = 0. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray 154 - 0. 174
Streak	White
Specific gravity	2. The streak (also called powder color) of a Mineral is the Color of the powder produced when it is dragged across an unweathered surface Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 71
Solubility	Soluble in dilute acids
Diaphaneity	Transparent to translucent
Other Characteristics	May fluoresce red, blue, yellow, and other colors under either SW and LW UV; phosphorescent
References	[1][2][3]

The unit cell of calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO₃). Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. Carbonate minerals are those Minerals containing the Carbonate Ion: CO32- Polymorphism in Materials science is the ability of a solid material to exist in more than one form or Crystal structure Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3 Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The other polymorphs are the minerals aragonite and vaterite. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Aragonite is a Carbonate mineral, one of the two common naturally occurring polymorphs of Calcium carbonate, Ca[[carbon C]] O 3 Vaterite ( Ca[[carbon C]] O 3 is a mineral a polymorph of Calcium carbonate. Aragonite will change to calcite at 470°C, and vaterite is even less stable.

Properties

fossil Seashell with calcite crystals

Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. A seashell, also known as a sea shell, is the Common name for a hard protective outer layer a shell or in some cases a " test " that was created In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating In Crystallography, the rhombohedral (or trigonal) Crystal system is one of the seven lattice point groups named after the two-dimensional However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms. Crystal twinning occurs when two separate crystals share some of the same Crystal lattice points in a symmetrical manner It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form. Its fracture is conchoidal, but difficult to obtain.

It has a Mohs hardness of 3, a specific gravity of 2. The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 71, and its luster is vitreous in crystallized varieties. Color is white or none, though shades of gray, red, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities.

Calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. Phosphorescence is a specific type of Photoluminescence related to fluorescence. Fluorescence is a Luminescence that is mostly found as an It is perhaps best known because of its power to produce strong double refraction of light, such that objects viewed through a clear piece of calcite appear doubled in all of their parts—a phenomenon first described by Rasmus Bartholin. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray Rasmus Bartholin (Latinized Erasmus Bartholinus; August 13, 1625, Roskilde - † November 4, 1698, Kopenhagen A beautifully transparent variety used for optical purposes comes from Iceland, called Iceland spar. Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( Iceland spar, formerly known as Iceland crystal, is a transparent variety of Calcite, or crystallized Calcium carbonate, originally brought from Iceland Acute scalenohedral crystals are sometimes referred to as "dogtooth spar".

Single calcite crystals display an optical property called birefringence. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray The birefringent effect (using calcite) was first described by the Danish scientist Rasmus Bartholin in 1669. The Kingdom of Denmark ( ˈd̥ænmɑɡ̊ (archaic ˈd̥anmɑːɡ̊ commonly known as Denmark, is a country in the Scandinavian region of northern Europe Rasmus Bartholin (Latinized Erasmus Bartholinus; August 13, 1625, Roskilde - † November 4, 1698, Kopenhagen At a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 658 and 1. 486, respectively^[4]. Between 190 and 1700 nm, the ordinary refractive index varies roughly between 1. 6 and 1. 4, while the extraordinary refractive index varies between 1. 9 and 1. 5^[5].

Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Solvation, commonly called dissolution, is the process of attraction and association of Molecules of a Solvent with molecules or Ions of a Precipitation is the formation of a Solid in a Solution during a Chemical reaction. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Although calcite is fairly insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. When conditions are right for dissolution, the removal of calcite can dramatically increase the porosity and permeability of the rock, and if it continues for a long period of time may result in the formation of caverns. Porosity is a measure of the void spaces in a material and is measured as a fraction between 0–1 or as a Percentage between 0–100% Permeability in the Earth sciences (commonly symbolized as κ, or k) is a measure of the ability of a material (typically a rock or unconsolidated A cave is a natural underground void large enough for a human to enter

Natural occurrence

Calcite is often the primary constituent of the shells of marine organisms, e. A seashell, also known as a sea shell, is the Common name for a hard protective outer layer a shell or in some cases a " test " that was created Marine biology is the scientific study of living Organisms in the Ocean or other marine or Brackish bodies of water g. , plankton (such as coccoliths and planktic foraminifera), the hard parts of red algae, some sponges, brachiopoda, echinoderms, most bryozoa, and parts of the shells of some bivalves, such as oysters and rudists). Plankton consist of any drifting Organisms ( Animals Plants Archaea, or Bacteria) that inhabit the Pelagic zone of Coccoliths are individual plates of Calcium carbonate formed by Coccolithophores (single-celled algae such as Emiliania huxleyi The Foraminifera, ("Hole Bearers" or forams for short are a large group of Amoeboid Protists with reticulating Pseudopods fine Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals Brachiopods (from Latin brachium, arm + New Latin -poda, foot are a small phylum of Benthic Invertebrates Also Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some Bivalves are Molluscs belonging to the class Bivalvia. They have two-part shells and typically both valves are symmetrical along the hinge line The common name oyster is used for a number of different groups of Bivalve Mollusks most of which live in marine habitats or Brackish water. Rudists are a group of bizarrely shaped marine Heterodont Bivalves that arose during the Jurassic, and became so diverse during the

Calcite is a common constituent of sedimentary rocks, limestone in particular, much of which is formed from the shells of dead marine organisms. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Approximately 10% of sedimentary rock is limestone.

Calcite is the primary mineral in metamorphic marble. Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change Marble is a nonfoliated Metamorphic rock resulting from the Metamorphism of Limestone, composed mostly of Calcite (a crystalline form of It also occurs as a vein mineral in deposits from hot springs, and it occurs in caverns as stalactites and stalagmites. In Geology, a vein is a finite volume within a rock, having a distinct shape filled with Crystals of one or more Minerals which were precipitated A hot spring is a spring that is produced by the emergence of geothermally heated Groundwater from the earth's crust. A cave is a natural underground void large enough for a human to enter A stalactite ( Greek stalaktites, (Σταλακτίτης from the word for "drip" and meaning "that which drips" is a type of Speleothem A stalactite ( Greek stalaktites, (Σταλακτίτης from the word for "drip" and meaning "that which drips" is a type of Speleothem

Calcite may also be found in volcanic or mantle-derived rocks such as carbonatites, kimberlites, or rarely in peridotites. Plate tectonics and hotspots Divergent plate boundaries At the The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided Carbonatites (kɑrˈbɒnətaɪt are Intrusive or extrusive Igneous rocks defined by mineralogy that comprises more than 50 volume-% Carbonate Kimberlite is a type of potassic Volcanic rock best known for sometimes containing Diamonds It is named after the town of Kimberley in South Africa A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene.

Calcite in Earth history

Calcite seas existed in Earth 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. A calcite sea is one in which low-magnesium Calcite is the primary inorganic marine Calcium carbonate precipitate Aragonite is a Carbonate mineral, one of the two common naturally occurring polymorphs of Calcium carbonate, Ca[[carbon C]] O 3 Calcite seas alternated with aragonite seas over the Phanerozoic, being most prominent in the Ordovician and Jurassic. The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning Petrographic evidence for these calcite sea conditions consists of calcitic ooids, lmc cements, hardgrounds, and rapid early seafloor aragonite dissolution. Petrography is that branch of Petrology which focuses on detailed descriptions of rocks. Ooids are small ( Sedimentary grains usually composed of Calcium carbonate, but sometimes made up of Iron Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer 1992 ^[6] The evolution of marine organisms with calcium carbonate shells may have been affected by the calcite and aragonite sea cycle. ^[7]

Calcite In Literature

A form of calcite, Iceland spar, plays a critical role in the plot of Against the Day by Thomas Pynchon. Iceland spar, formerly known as Iceland crystal, is a transparent variety of Calcite, or crystallized Calcium carbonate, originally brought from Iceland Against the Day is a Novel by Thomas Pynchon. The Narrative takes place between the 1893 Chicago World's Fair and the time immediately Thomas Ruggles Pynchon Jr (born May 8 1937 is an American writer based in New York City, noted for his dense and complex works of Fiction. The same form is referred to in The Amber Spyglass by Philip Pullman as it has very similar properties to a mineral found in that story. The Amber Spyglass is the third and final Novel in the His Dark Materials series written by English Author Philip Pullman CBE (born October 19, 1946) is an English writer.

See also

• Monohydrocalcite, CaCO₃·H₂O
• Ikaite, CaCO₃·6H₂O
• Manganoan Calcite, (Ca,Mn)CO₃
• List of minerals
• Lysocline
• Ocean acidification

References

1. ^ http://rruff.geo.arizona.edu/doclib/hom/calcite.pdf Mineral Data Publishers
2. ^ http://www.mindat.org/min-859.html Mindat
3. ^ http://webmineral.com/data/Calcite.shtml Webmineral data
4. ^ Elert, Glenn. Monohydrocalcite is a mineral that is a hydrous form of Calcium carbonate, CaCO3·H2O Ikaite is the mineral name for the hexahydrate of Calcium carbonate, CaCO3·6H2O thumb|'''Manganocalcite''' Manganoan Calcite or Manganocalcite is a variety of Calcite rich in Manganese, which gives the mineral a pink This is a List of Minerals for which there are Wikipedia articles The lysocline is a term used in Geology, Geochemistry and Marine biology to denote the depth in the Ocean below which the rate of dissolution Refraction. The Physics Hypertextbook.
5. ^ Thompson, D. W. et al 1998. Determination of optical anisotropy in calcite from ultraviolet to mid-infrared by generalized ellipsometry. Thin Solid Films 313-314 (1998) 341-346. http://dx.doi.org/10.1016/S0040-6090(97)00843-2
6. ^ Palmer, T. J. and Wilson, M. A. 2004. Calcite precipitation and dissolution of biogenic aragonite in shallow Ordovician calcite seas. Lethaia 37: 417-427. http://www.wooster.edu/geology/PalmerWilson05.pdf
7. ^ Harper, E. M. , Palmer, T. J. and Alphey, J. R. 1997. Evolutionary response by bivalves to changing Phanerozoic sea-water chemistry. Geological Magazine 134: 403-407

• Calcite information and images

Further reading

• Schmittner Karl-Erich and Giresse Pierre, 1999. Micro-environmental controls on biomineralization: superficial processes of apatite and calcite precipitation in Quaternary soils, Roussillon, France. Sedimentology 46/3: 463-476.

External links

• Information about the largest and most famous calcite crystals