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Calcium carbonate is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical bonds. A homonuclear molecule, m ...
with the
formula In , a formula is a concise way of expressing information symbolically, as in a mathematical formula or a . The informal use of the term ''formula'' in science refers to the . The plural of ''formula'' can be either ''formulas'' (from the mos ...
Ca
Ca
CO3
CO<sub>3</sub>
. It is a common substance found in
rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proc ...
as the
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
s
calcite Calcite is a and the most stable of (CaCO3). The , based on , defines value 3 as "calcite". Other polymorphs of calcium carbonate are the minerals and . Aragonite will change to calcite over timescales of days or less at temperatures exceed ...

calcite
and
aragonite Aragonite is a , one of the three most common naturally occurring of , (the other forms being the s and ). It is formed by biological and physical processes, including precipitation from marine and freshwater environments. The of aragonite d ...

aragonite
(most notably as
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
, which is a type of sedimentary rock consisting mainly of calcite) and is the main component of
eggshell An eggshell is the outer covering of a hard-shelled egg Diagram of a chicken egg in its 9th day. Membranes: allantois, chorion, amnion, and vitellus/ yolk. An egg is the organic vessel containing the zygote in which an embryo develops u ...

eggshell
s,
snail A snail is, in loose terms, a shelled gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (co ...

snail
shells,
seashell A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beach ...

seashell
s and
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle (mollusc), mantle) of a living animal shell, shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pe ...

pearl
s. Calcium carbonate is the active ingredient in
agricultural lime Agricultural lime, also called aglime, agricultural limestone, garden lime or liming, is a soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases ...
and is created when calcium ions in
hard water Hard water is water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living orga ...
react with
carbonate ion In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline min ...
s to create
limescale Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of old ...
. It has medical use as a
calcium Calcium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

calcium
supplement or as an
antacid An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn Heartburn, also known as pyrosis, cardialgia or acid indigestion, is a burning sensation in the central chest or upper central abdomen. The disc ...
, but excessive consumption can be hazardous and cause
hypercalcemia Hypercalcemia, also spelled hypercalcaemia, is a high calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride ...
and digestive issues.


Chemistry

Calcium carbonate shares the typical properties of other carbonates. Notably it * reacts with
acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the proton donors, or s. In the special case of , proton donors form the H3O+ and are ...
s, releasing
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
(technically speaking,
carbonic acid In chemistry, carbonic acid is a dibasic acid with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical ...

carbonic acid
, but that disintegrates quickly to CO2 and H2O): ::CaCO3() + 2 H+() → Ca2+() + CO2() + H2O() * releases carbon dioxide upon heating, called a
thermal decomposition Thermal decomposition, or thermolysis, is a chemical decompositionChemical decomposition, or chemical breakdown, is the process or effect of simplifying a single chemical entity (normal molecule, reaction intermediate, etc.) into two or more fra ...
reaction, or
calcination Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment Thermal treatment is any ...
(to above 840 °C in the case of CaCO3), to form
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter ...

calcium oxide
, commonly called
quicklime Calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical pr ...
, with reaction
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant p ...

enthalpy
178 kJ/mol: ::CaCO3() → CaO() + CO2() Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble
calcium bicarbonate Calcium bicarbonate, also called calcium hydrogen carbonate, has a chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing the calcium (Ca2+), bicarbonate (), and carbonate () io ...

calcium bicarbonate
. :CaCO3() + CO2() + H2O() → Ca(HCO3)2() This reaction is important in the
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
of
carbonate rock 250px, Carbonate ooids on the surface of a limestone; Carmel Formation (Middle Jurassic) of southern Utah, USA. Largest is 1.0 mm in diameter. Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major ...
, forming
cavern A cave or cavern is a natural void in the ground Ground may refer to: * Soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, an ...

cavern
s, and leads to
hard water Hard water is water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living orga ...
in many regions. An unusual form of calcium carbonate is the hexahydrate,
ikaite Ikaite is the mineral name for the hexahydrate of calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone ...
, CaCO3·6H2O. Ikaite is stable only below 8 °C.


Preparation

The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (such as for food or pharmaceutical use), can be produced from a pure quarried source (usually
marble Marble is a metamorphic rock , a type of metamorphic rock Metamorphic rocks arise from the transformation of existing rock (geology), rock to new types of rock, in a process called metamorphism upright=1.35, Schematic representation of ...

marble
). Alternatively, calcium carbonate is prepared from
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter ...

calcium oxide
. Water is added to give
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula calcium, Ca(Hydroxide, OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaking (ge ...

calcium hydroxide
then
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC): :CaO + H2O → Ca(OH)2 :Ca(OH)2 + CO2 → CaCO3↓ + H2O


Structure

The thermodynamically stable form of CaCO3 under normal conditions is
hexagonal In geometry, a hexagon (from Ancient Greek, Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon or 6-gon. The total of the internal angles of any simple polygon, simple (non-self-intersecting) hexagon is 720°. Regul ...
β-CaCO3 (the mineral
calcite Calcite is a and the most stable of (CaCO3). The , based on , defines value 3 as "calcite". Other polymorphs of calcium carbonate are the minerals and . Aragonite will change to calcite over timescales of days or less at temperatures exceed ...

calcite
). Other forms can be prepared, the denser (2.83 g/cm3)
orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism An ...

orthorhombic
λ-CaCO3 (the mineral
aragonite Aragonite is a , one of the three most common naturally occurring of , (the other forms being the s and ). It is formed by biological and physical processes, including precipitation from marine and freshwater environments. The of aragonite d ...

aragonite
) and hexagonal μ-CaCO3, occurring as the mineral
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) and has a JCPDS number of 13-192. Vaterite belongs to the hexagona ...

vaterite
. The aragonite form can be prepared by precipitation at temperatures above 85 °C, the vaterite form can be prepared by precipitation at 60 °C. Calcite contains calcium atoms coordinated by six oxygen atoms, in aragonite they are coordinated by nine oxygen atoms. The vaterite structure is not fully understood.
Magnesium carbonate Magnesium carbonate, Mg CO3 (archaic name magnesia alba), is an inorganic salt that is a white solid. Several hydrate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, com ...

Magnesium carbonate
(MgCO3) has the calcite structure, whereas
strontium carbonate Strontium carbonate (SrCO3) is the carbonate salt of strontium Strontium is the chemical element with the symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, Object (philosophy), obje ...

strontium carbonate
and
barium carbonate Barium carbonate is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is not clearly defin ...

barium carbonate
(SrCO3 and BaCO3) adopt the aragonite structure, reflecting their larger .


Occurrence


Geological sources

Calcite Calcite is a carbonate mineral Carbonate minerals are those mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid E ...

Calcite
,
aragonite Aragonite is a , one of the three most common naturally occurring of , (the other forms being the s and ). It is formed by biological and physical processes, including precipitation from marine and freshwater environments. The of aragonite d ...

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) and has a JCPDS number of 13-192. Vaterite belongs to the hexagona ...

vaterite
are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
,
chalk Chalk is a soft, white, porous Porosity or void fraction is a measure of the (i.e. "empty") spaces in a , and is a of voids over the total volume, between 0 and 1, or as a between 0% and 100%. Strictly speaking, some tests measure the "acce ...

chalk
,
marble Marble is a metamorphic rock , a type of metamorphic rock Metamorphic rocks arise from the transformation of existing rock (geology), rock to new types of rock, in a process called metamorphism upright=1.35, Schematic representation of ...

marble
and
travertine Travertine ( ) is a form of terrestrial limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the l ...

travertine
.


Biological sources

Eggshell An eggshell is the outer covering of a hard-shelled egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excludi ...
s,
snail A snail is, in loose terms, a shelled gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (co ...

snail
shells and most
seashell A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beach ...

seashell
s are predominantly calcium carbonate and can be used as industrial sources of that chemical.
Oyster Oyster is the common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is sometim ...

Oyster
shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source. Dark
green vegetables Leaf vegetables, also called leafy greens, salad greens, pot herbs, vegetable greens, or simply greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. Although they come from a very wide variety ...
such as
broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the Brassicaceae, cabbage family (family Brassicaceae, genus ''Brassica'') whose large Pseudanthium, flowering head, plant stem, stalk and small associated leafy green ...

broccoli
and
kale Kale (), or leaf cabbage, belongs to a group of cabbage (''Brassica oleracea ''Brassica oleracea'' is a plant species that includes many common foods as cultivars, including cabbage, broccoli, cauliflower, kale, Brussels sprouts, collard gree ...

kale
contain dietarily significant amounts of calcium carbonate, but they are not practical as an industrial source.


Extraterrestrial

Beyond Earth, strong evidence suggests the presence of calcium carbonate on
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries the name of the Mars (mythology), Roman god of war and is often referred to ...

Mars
. Signs of calcium carbonate have been detected at more than one location (notably at and Huygens craters). This provides some evidence for the past presence of liquid water.


Geology

Carbonate is found frequently in geologic settings and constitutes an enormous . Calcium carbonate occurs as
aragonite Aragonite is a , one of the three most common naturally occurring of , (the other forms being the s and ). It is formed by biological and physical processes, including precipitation from marine and freshwater environments. The of aragonite d ...

aragonite
,
calcite Calcite is a and the most stable of (CaCO3). The , based on , defines value 3 as "calcite". Other polymorphs of calcium carbonate are the minerals and . Aragonite will change to calcite over timescales of days or less at temperatures exceed ...

calcite
and
dolomiteDolomite may refer to: *Dolomite (mineral) Dolomite () is an anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and ...
as significant constituents of the calcium cycle. The
carbonate mineral Carbonate minerals are those mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of ...
s form the rock types:
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
,
chalk Chalk is a soft, white, porous Porosity or void fraction is a measure of the (i.e. "empty") spaces in a , and is a of voids over the total volume, between 0 and 1, or as a between 0% and 100%. Strictly speaking, some tests measure the "acce ...

chalk
,
marble Marble is a metamorphic rock , a type of metamorphic rock Metamorphic rocks arise from the transformation of existing rock (geology), rock to new types of rock, in a process called metamorphism upright=1.35, Schematic representation of ...

marble
,
travertine Travertine ( ) is a form of terrestrial limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the l ...

travertine
,
tufa Tufa is a variety of limestone formed when carbonate minerals precipitation (chemistry), precipitate out of ambient temperature water. hot spring, Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits, w ...
, and others. In warm, clear tropical waters
coral Corals are marine invertebrates Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a ver ...

coral
s are more abundant than towards the poles where the waters are cold. Calcium carbonate contributors, including
plankton Plankton are the diverse collection of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by tax ...

plankton
(such as
coccolith Coccoliths are individual plates of calcium carbonate formed by coccolithophores (single-celled algae such as '' Emiliania huxleyi'') which are arranged around them in a ''coccosphere''. Formation and composition Coccoliths are formed within t ...
s and planktic
foraminifera Foraminifera (; Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...
),
coralline algae Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of red ...

coralline algae
,
sponges Sponges, the members of the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. T ...

sponges
,
brachiopod Brachiopods (), phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a ...
s,
echinoderm An echinoderm () is any member of the phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of ...
s,
bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the ...

bryozoa
and
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil species is es ...

mollusks
, are typically found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate. The
calcification Calcification is the accumulation of calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when expose ...
processes are changed by
ocean acidification Ocean acidification is the ongoing decrease in the pH value of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of cont ...
. Where the
oceanic crust The oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust 350px, Plates in the crust of Earth Earth's crust i ...
is
subducted Subduction is a geological process in which the oceanic lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On ...

subducted
under a
continental plate Continental may refer to: Places * Continent * Continental, Arizona, a small community in Pima County, Arizona, US * Continental, Ohio, a small town in Putnam County, US Arts and entertainment * Continental (album), ''Continental'' (album), an alb ...
sediments will be carried down to warmer zones in the
asthenosphere The asthenosphere ( grc, ἀσθενός 'asthenos''meaning "without strength", and thus "weak", and 'sphaira''meaning "sphere") is the highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Defor ...
and
lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion o ...
. Under these conditions calcium carbonate decomposes to produce
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
which, along with other gases, give rise to explosive
volcanic eruptions Several types of volcanic eruptions—during which lava of pāhoehoe lava, Hawaii, United States , Iceland in 1984 Lava is molten Rock (geology), rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) ...

volcanic eruptions
.


Carbonate compensation depth

The
carbonate compensation depth Carbonate compensation depth (CCD) is the depth in the oceans below which the rate of supply of calcite Image:Calcite.png, 235px, Crystal structure of calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (mat ...
(CCD) is the point in the ocean where the rate of precipitation of calcium carbonate is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature drops and pressure increases. Calcium carbonate is unusual in that its solubility increases with decreasing temperature. Increasing pressure also increases the solubility of calcium carbonate. The carbonate compensation depth can range from 4,000 to 6,000 meters below sea level.


Role in taphonomy

Calcium carbonate can preserve fossils through
permineralization Permineralization is a process of fossil A fossil (from Classical Latin: , literally "obtained by digging") is any preserved remains, impression, or trace of any once- living thing from a past geological age. Examples include bones, shell ...

permineralization
. Most of the vertebrate fossils of the
Two Medicine Formation The Two Medicine Formation is a geologic formation, or rock body, in northwestern Montana and southern Alberta that was deposited between and (million years ago), during Campanian (Late Cretaceous) time. It crops out to the east of the Rocky Mount ...
—a
geologic formation A geological formation, or formation, is a body of rock having a consistent set of physical characteristics (lithology as seen in southeastern Utah The lithology of a Rock (geology), rock unit is a description of its physical characteristics vis ...
known for its duck-billed dinosaur eggs—are preserved by CaCO3 permineralization. This type of preservation conserves high levels of detail, even down to the microscopic level. However, it also leaves specimens vulnerable to
weathering Weathering is the deterioration of Rock (geology), rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little o ...
when exposed to the surface.
Trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the 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 of the ( ...

Trilobite
populations were once thought to have composed the majority of aquatic life during the
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
, due to the fact that their calcium carbonate-rich shells were more easily preserved than those of other species, which had purely
chitin units that repeat to form long chains in β-(1→4)-linkage. of the chitin molecule. Chitin ( carbon, C8H13O5N)n ( ) is a long-chain polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical su ...

chitin
ous shells.


Uses


Industrial applications

The main use of calcium carbonate is in the construction industry, either as a building material, or limestone aggregate for road building, as an ingredient of
cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (constru ...
, or as the starting material for the preparation of builders' lime by burning in a
kiln , Wrecclesham Wrecclesham is a village on the southern outskirts of the large town of Farnham Farnham is a market town in Surrey, England, within the Borough of Waverley Borough Council, Waverley.OS Explorer map 145:Guildford and Farnham ...

kiln
. However, because of weathering mainly caused by
acid rain Acid rain is a rain or any other form of Precipitation (meteorology), precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals, and infras ...
, calcium carbonate (in limestone form) is no longer used for building purposes on its own, but only as a raw primary substance for building materials. Calcium carbonate is also used in the purification of
iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

iron
from
iron ore Iron ores are rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it i ...
in a
blast furnace A blast furnace is a type of used for to produce industrial metals, generally , but also others such as or . ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric pressure. In a blast furnace, fuel (), , and ( ...
. The carbonate is
calcined Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment process in the absence o ...
''in situ'' to give
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter ...

calcium oxide
, which forms a
slag Slag is a by-product of smelting Smelting is a process of applying heat to ore ore – psilomelane (size: 6.7 × 5.8 × 5.1 cm) ore – galena and anglesite (size: 4.8 × 4.0 × 3.0 cm) ore (size: 7.5 × 6.1 × 4.1 cm) File: ...

slag
with various impurities present, and separates from the purified iron. In the
oil industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration Exploration is the act of searching for the purpose of discovery Discovery may refer to: * Discovery (observation) Disc ...
, calcium carbonate is added to
drilling fluid Driller pouring anti-foaming agent down the drilling string on a drilling rig In geotechnical engineering#REDIRECT geotechnical engineering {{Redirect category shell, 1= {{R from other capitalisation ..., drilling fluid, also called drilli ...
s as a formation-bridging and filtercake-sealing agent; it is also a weighting material which increases the density of drilling fluids to control the downhole pressure. Calcium carbonate is added to
swimming pool A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable Human swimming, swimming or other leisure activities. Pools can be built into the ground (in-ground pools) or built ...

swimming pool
s, as a corrector for maintaining
alkalinity Alkalinity (from Arabic "''al-qalī''") is the capacity of water to resist acidification. It should not be confused with basicity which is an absolute measurement on the pH scale. Alkanity is the strength of a buffer solution composed of weak ...
and offsetting the acidic properties of the
disinfectant A disinfectant is a chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
agent. It is also used as a raw material in the refining of sugar from
sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose Sucrose is a type of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated ...
; it is calcined in a kiln with
anthracite Anthracite, also known as hard coal, is a hard, compact variety of coal that has a lustre (mineralogy)#Submetallic lustre, submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of ...

anthracite
to produce calcium oxide and carbon dioxide. This burnt lime is then slaked in fresh water to produce a calcium hydroxide
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...
for the precipitation of impurities in raw juice during
carbonatation Carbonatation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter ...
. Calcium carbonate in the form of
chalk Chalk is a soft, white, porous Porosity or void fraction is a measure of the (i.e. "empty") spaces in a , and is a of voids over the total volume, between 0 and 1, or as a between 0% and 100%. Strictly speaking, some tests measure the "acce ...

chalk
has traditionally been a major component of
blackboard A blackboard (also known as a chalkboard) is a reusable surface on which text or drawings are made with sticks of or , known, when used for this purpose, as . Blackboards were originally made of smooth, thin sheets of or dark grey stone. ...

blackboard
chalk. However, modern manufactured chalk is mostly
gypsum Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

gypsum
, hydrated
calcium sulfate Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrate In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that cove ...

calcium sulfate
CaSO4·2H2O. Calcium carbonate is a main source for growing . Precipitated calcium carbonate (PCC), pre-dispersed in
slurry A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids, the liquid being a carrier that is pumped on a device such as a . The size of solid particles may vary ...
form, is a common filler material for
latex gloves Medical gloves are disposable glove A glove is a garment A kanga, worn throughout the African Great Lakes region Clothing (also known as clothes, apparel and attire) are items worn on the body. Clothing is typically made of fabrics or ...
with the aim of achieving maximum saving in material and production costs. Fine ground calcium carbonate (GCC) is an essential ingredient in the microporous film used in
diapers A diaper /ˈdaɪpə(r)/ (American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of America (USA), commonly known as the ...
and some building films, as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching. GCC and PCC are used as a filler in
paper Paper is a thin sheet material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition ...

paper
because they are cheaper than
wood fiber Wood fibres (also spelled wood fibers, see spelling differences) are usually cellulosic elements that are extracted from trees and used to make materials including paper Paper is a thin sheet material produced by mechanically and/or chemica ...
. In terms of market volume, GCC are the most important types of fillers currently used. Printing and writing paper can contain 10–20% calcium carbonate. In North America, calcium carbonate has begun to replace
kaolin Kaolinite ( ) is a clay mineral Clay minerals are , sometimes with variable amounts of , , s, s, and other s found on or near some s. Clay minerals form in the presence of water and have been important to life, and many theories of in ...

kaolin
in the production of
glossy paperCoated paper (also known as enamel paper, gloss paper, and slick paper) is paper that has been coating, coated by a mixture of materials or a polymer to impart certain qualities to the paper, including weight, surface gloss, smoothness, or reduced in ...
. Europe has been practicing this as alkaline
papermaking Papermaking is the manufacture of paper and cardboard, which are used widely for printing, writing, and packaging, among many other purposes. Today almost all paper is Pulp and paper industry, made using industrial machinery, while handmade pape ...
or acid-free papermaking for some decades. PCC used for paper filling and paper coatings is precipitated and prepared in a variety of shapes and sizes having characteristic narrow particle size distributions and equivalent spherical diameters of 0.4 to 3 micrometers. Calcium carbonate is widely used as an extender in
paint Paint is any pigmented liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned wi ...

paint
s, in particular matte
emulsion paint Paint is any pigmented liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a Phase ...
where typically 30% by weight of the paint is either chalk or marble. It is also a popular filler in plastics. Some typical examples include around 15 to 20% loading of chalk in
unplasticized polyvinyl chloride Polyvinyl chloride (colloquial: polyvinyl, Vinyl polymer, vinyl; abbreviated: PVC) is the world's third-most widely produced synthetic plastic polymer (after polyethylene and polypropylene). About 40 million tons of PVC are produced each year. ...
(uPVC) , 5% to 15% loading of -coated chalk or marble in uPVC window profile.
PVC Polyvinyl chloride (colloquial Colloquialism or colloquial language is the style (sociolinguistics), linguistic style used for casual communication. It is the most common functional style of speech, the idiom normally employed in conversatio ...
cables can use calcium carbonate at loadings of up to 70 phr (parts per hundred parts of resin) to improve mechanical properties (tensile strength and elongation) and electrical properties (volume resistivity).
Polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic A thermoplastic, or thermosoftening plastic, is a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most the ...

Polypropylene
compounds are often filled with calcium carbonate to increase rigidity, a requirement that becomes important at high usage temperatures. Here the percentage is often 20–40%. It also routinely used as a filler in thermosetting resins (sheet and bulk molding compounds) and has also been mixed with ABS, and other ingredients, to form some types of compression molded "clay"
poker chip Casino tokens (also known as casino or gaming chips, checks, or cheques) are small discs used in lieu of currency in casinos. Colored metal, injection-molded plastic or compression molded clay tokens of various denominations are used primarily i ...
s. Precipitated calcium carbonate, made by dropping
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter ...

calcium oxide
into water, is used by itself or with additives as a white paint, known as
whitewash Three different brands of kalsomine Whitewash, or calcimine, kalsomine, calsomine, or lime paint is a type of paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin ...
ing. Calcium carbonate is added to a wide range of trade and
do it yourself "Do it yourself" ("DIY") is the method of building, wikt:modification, modifying, or repairing things by themself without the direct aid of experts or professionals. Academic research has described DIY as behaviors where "individuals engage R ...
adhesives, sealants, and decorating fillers. Ceramic tile adhesives typically contain 70% to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting
stained glass File:Oostende Sint-Petrus-en-Pauluskerk Rosette.jpg, 300px, Outside-view of a stained glass of the Sint-Petrus-en-Pauluskerk from Ostend (Belgium), built between 1899 and 1908 The term stained glass refers to coloured glass as a material and to ...

stained glass
windows, and as a resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature. In
ceramic glaze Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a pottery Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired ...
applications, calcium carbonate is known as ''whiting'', and is a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a
flux of \mathbf(\mathbf) with the unit normal vector \mathbf(\mathbf) ''(blue arrows)'' at the point \mathbf multiplied by the area dS. The sum of \mathbf\cdot\mathbf dS for each patch on the surface is the flux through the surface Flux describes ...
material in the glaze. Ground calcium carbonate is an
abrasive An abrasive is a material, often a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs n ...
(both as scouring powder and as an ingredient of household scouring creams), in particular in its calcite form, which has the relatively low hardness level of 3 on the
Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale Ordinal data is a categorical, statistical data type where the variables have natural, ordered categories and the distances between the categories are not known. These data e ...
, and will therefore not scratch
glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by ...

glass
and most other
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant Corrosion is a Erosion, natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulfide. ...

ceramic
s, enamel,
bronze Bronze is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appear ...

bronze
,
iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

iron
, and
steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appe ...

steel
, and have a moderate effect on softer metals like
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
and
copper Copper is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

copper
. A paste made from calcium carbonate and
deionized water Image:Aqua-distillata.jpg, 200px, Bottle for distilled water in the Royal Academy of Pharmacy, Royal Academy of Pharmacy (Spain) Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for ...
can be used to clean
tarnish Tarnish is a thin layer of corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide of rutile. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds ...
on
silver Silver is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

silver
.


Health and dietary applications

Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement for gastric antacid (such as
Tums Tums (stylized as TUMS) is an antacid made of sucrose (sugar) and calcium carbonate (CaCO3) manufactured by GlaxoSmithKline in St. Louis, Missouri, US. They are also available in a sugar-free version. It is an over-the-counter drug, available at ...
). It may be used as a
phosphate binderPhosphate binders are medications used to reduce the absorption of dietary phosphate; they are taken along with meals and snacks. They are frequently used in people with chronic kidney failure (CKF), who are less able to excrete phosphate, resulting ...
for the treatment of
hyperphosphatemia Hyperphosphatemia is an electrolyte disorder in which there is an elevated level of phosphate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of ato ...
(primarily in patients with
chronic kidney failure Chronic kidney disease (CKD) is a type of kidney disease The kidneys are two reddish-brown bean-shaped organs found in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukary ...
). It is used in the pharmaceutical industry as an inert filler for tablets and other
pharmaceuticals A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, therapy, treat, or preventive medicine, prevent disease. Drug therapy (pharmacotherapy) ...
. Calcium carbonate is used in the production of calcium oxide as well as toothpaste and has seen a resurgence as a food preservative and color retainer, when used in or with products such as organic apples. Calcium carbonate is used therapeutically as phosphate binder in patients on maintenance
haemodialysis Hemodialysis, also spelled haemodialysis, or simply dialysis, is a process of purifying the blood of a person whose kidneys are not working normally. This type of dialysis achieves the extracorporeal removal of waste products such as creatinin ...
. It is the most common form of phosphate binder prescribed, particularly in non-dialysis chronic kidney disease. Calcium carbonate is the most commonly used phosphate binder, but clinicians are increasingly prescribing the more expensive, non-calcium-based phosphate binders, particularly
sevelamer Sevelamer ( rINN) is a phosphate binding medication used to treat hyperphosphataemia, hyperphosphatemia in patients with chronic kidney disease. When taken with meals, it binds to dietary phosphate and prevents its absorption. Sevelamer was invent ...

sevelamer
. Excess calcium from supplements, fortified food, and high-calcium diets can cause
milk-alkali syndrome In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment or Palliative care , palliation of their i ...
, which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, and the gradual addition of eggs and cooked cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in
kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys are functioning at less than 15% of normal levels. Kidney failure is classified as either acute kidney failure, which develops rapidly and may res ...
,
alkalosis Alkalosis is the result of a process reducing hydrogen ion A hydrogen ion is created when a hydrogen atom loses or gains an electron. A positively charged hydrogen ion (or proton) can readily combine with other particles and therefore is only seen ...
, and
hypercalcaemia Hypercalcaemia, also spelled hypercalcemia, is a high calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride ...
, mostly in men with peptic ulcer disease. These adverse effects were reversed when the regimen stopped, but it was fatal in some patients with protracted vomiting. Milk-alkali syndrome declined in men after effective treatments for
peptic ulcer Peptic ulcer disease (PUD) is a break in the inner Gastric mucosa, lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of t ...

peptic ulcer
disease arose. Since the 1990s it has been most frequently reported in women taking calcium supplements above the recommended range of 1.2 to 1.5 grams daily, for prevention and treatment of osteoporosis, and is exacerbated by
dehydration In physiology, dehydration is a lack of total body water In physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studies ...

dehydration
. Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake. Excessive calcium intake can lead to
hypercalcemia Hypercalcemia, also spelled hypercalcaemia, is a high calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride ...
, complications of which include vomiting, abdominal pain and altered mental status. As a
food additive Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology ...
it is designated
E170E170 may refer to: * Model E-170 Regional Jet, see Embraer E-Jets * The E number of a food additive or colouring for calcium carbonate or chalk * Toyota Corolla (E170), a car {{Letter-NumberCombDisambig ...
, and it has an INS number of 170. Used as an
acidity regulator Acidity regulators, or pH control agents, are food additives used to change or maintain pH ( acidity or basicity). They can be organic or mineral acids, bases, neutralizing agents, or buffering agents. Typical agents include the following ...
,
anticaking agentAn anticaking agent is an additive Additive may refer to: Mathematics * Additive function In number theory, an additive function is an arithmetic function ''f''(''n'') of the positive integer ''n'' such that whenever ''a'' and ''b'' are coprime, ...
,
stabilizer Stabilizer, stabiliser, stabilisation or stabilization may refer to: Chemistry and food processing * Stabilizer (chemistry), a substance added to prevent unwanted change in state of another substance ** Polymer stabilizers are stabilizers used s ...
or
color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Engli ...

color
it is approved for usage in the EU, USA and
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
and
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
. It is "added by law to all UK milled bread flour except wholemeal". It is used in some
soy milk Soya milk (simplified Chinese Simplified Chinese characters are standardized Chinese characters Chinese characters, also called ''Hanzi'' (), are logograms developed for the writing of Chinese. They have been adapted to write o ...

soy milk
and
almond milk Almond milk is a plant milk manufactured from almonds with a creamy texture and nutty flavor, although some types or brands are flavored in imitation of dairy milk. It does not contain cholesterol Cholesterol (from the Ancient Greek ...
products as a source of dietary calcium; at least one study suggests that calcium carbonate might be as
bioavailable In pharmacology Pharmacology is a branch of medicine and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a bio ...
as the calcium in
cow's milk Milk is a nutrient-rich liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they are able to digestion, digest solid food. Earl ...
. Calcium carbonate is also used as a firming agent in many canned and bottled vegetable products.


Agricultural and Aquacultural use

Agricultural lime Agricultural lime, also called aglime, agricultural limestone, garden lime or liming, is a soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases ...
, powdered chalk or limestone, is used as a cheap method for neutralising
acidic soil Soil pH is a measure of the acidity or basicity In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases and Lewis bases. All definitions agree that bases are substances which reac ...
, making it suitable for planting, also used in aquaculture industry for ph regulation of pond soil before initiating culture.


Household use

Calcium carbonate is a key ingredient in many household cleaning powders like
Comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astr ...
and is used as a scrubbing agent.


Environmental applications

In 1989, a researcher, Ken Simmons, introduced CaCO3 into the Whetstone Brook in Massachusetts. His hope was that the calcium carbonate would counter the acid in the stream from acid rain and save the trout that had ceased to spawn. Although his experiment was a success, it did increase the amount of aluminium ions in the area of the brook that was not treated with the limestone. This shows that CaCO3 can be added to neutralize the effects of acid rain in river ecosystems. Currently calcium carbonate is used to neutralize acidic conditions in both soil and water. Since the 1970s, such ''liming'' has been practiced on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly. Calcium carbonate is also used in flue gas desulfurisation applications eliminating harmful SO2 and NO2 emissions from coal and other fossil fuels burnt in large fossil fuel power stations.


Calcination equilibrium

Calcination of
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
using charcoal fires to produce calcium oxide, quicklime has been practiced since antiquity by cultures all over the world. The temperature at which limestone yields calcium oxide is usually given as 825 °C, but stating an absolute threshold is misleading. Calcium carbonate exists in equilibrium with calcium oxide and
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
at any temperature. At each temperature there is a partial pressure of carbon dioxide that is in equilibrium with calcium carbonate. At room temperature the equilibrium overwhelmingly favors calcium carbonate, because the equilibrium CO2 pressure is only a tiny fraction of the partial CO2 pressure in air, which is about 0.035 kPa. At temperatures above 550 °C the equilibrium CO2 pressure begins to exceed the CO2 pressure in air. So above 550 °C, calcium carbonate begins to outgas CO2 into air. However, in a charcoal fired kiln, the concentration of CO2 will be much higher than it is in air. Indeed, if all the oxygen in the kiln is consumed in the fire, then the partial pressure of CO2 in the kiln can be as high as 20 kPa. The table shows that this partial pressure is not achieved until the temperature is nearly 800 °C. For the outgassing of CO2 from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of CO2. And for it to happen rapidly, the equilibrium pressure must exceed total atmospheric pressure of 101 kPa, which happens at 898 °C. :


Solubility


With varying CO2 pressure

Calcium carbonate is poorly soluble in pure water (47 mg/L at normal atmospheric CO2 partial pressure as shown below). The equilibrium of its solution is given by the equation (with dissolved calcium carbonate on the right): : where the solubility product for is given as anywhere from ''K''sp = to ''K''sp = at 25 °C, depending upon the data source. What the equation means is that the product of molar concentration of calcium ions (mole (unit), moles of dissolved Ca2+ per liter of solution) with the molar concentration of dissolved cannot exceed the value of ''K''sp. This seemingly simple solubility equation, however, must be taken along with the more complicated equilibrium of
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
with water (see
carbonic acid In chemistry, carbonic acid is a dibasic acid with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of atom An atom is the smallest unit of ordinary matter In classical ...

carbonic acid
). Some of the combines with H+ in the solution according to : is known as the bicarbonate ion. Calcium bicarbonate is many times more soluble in water than calcium carbonate—indeed it exists ''only'' in solution. Some of the combines with H+ in solution according to : Some of the H2CO3 breaks up into water and dissolved carbon dioxide according to : And dissolved carbon dioxide is in equilibrium with atmospheric carbon dioxide according to : For ambient air, ''P''CO2 is around atmospheres (or equivalently 35 Pascal (unit), Pa). The last equation above fixes the concentration of dissolved CO2 as a function of ''P''CO2, independent of the concentration of dissolved CaCO3. At atmospheric partial pressure of CO2, dissolved CO2 concentration is moles per liter. The equation before that fixes the concentration of H2CO3 as a function of CO2 concentration. For [CO2] = , it results in [H2CO3] = moles per liter. When [H2CO3] is known, the remaining three equations together with : (which is true for all aqueous solutions), and the fact that the solution must be electrically neutral, :2 [Ca2+] + [H+] = [] + 2 [] + [OH] make it possible to solve simultaneously for the remaining five unknown concentrations (note that the above form of the neutrality equation is valid only if calcium carbonate has been put in contact with pure water or with a neutral pH solution; in the case where the initial water solvent pH is not neutral, the equation is modified). The adjacent table shows the result for [Ca2+] and [H+] (in the form of pH) as a function of ambient partial pressure of CO2 (''K''sp = has been taken for the calculation). * At atmospheric levels of ambient CO2 the table indicates that the solution will be slightly alkaline with a maximum CaCO3 solubility of 47 mg/L. * As ambient CO2 partial pressure is reduced below atmospheric levels, the solution becomes more and more alkaline. At extremely low ''P''CO2, dissolved CO2, bicarbonate ion, and carbonate ion largely evaporate from the solution, leaving a highly alkaline solution of
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula calcium, Ca(Hydroxide, OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaking (ge ...

calcium hydroxide
, which is more soluble than CaCO3. Note that for ''P''CO2 = 10−12 atm, the product is still below the solubility product of Ca(OH)2 (). For still lower CO2 pressure, Ca(OH)2 precipitation will occur before CaCO3 precipitation. * As ambient CO2 partial pressure increases to levels above atmospheric, pH drops, and much of the carbonate ion is converted to bicarbonate ion, which results in higher solubility of Ca2+. The effect of the latter is especially evident in day-to-day life of people who have hard water. Water in aquifers underground can be exposed to levels of CO2 much higher than atmospheric. As such water percolates through calcium carbonate rock, the CaCO3 dissolves according to the second trend. When that same water then emerges from the tap, in time it comes into equilibrium with CO2 levels in the air by outgassing its excess CO2. The calcium carbonate becomes less soluble as a result, and the excess precipitates as lime scale. This same process is responsible for the formation of stalactites and stalagmites in limestone caves. Two hydrated phases of calcium carbonate, monohydrocalcite CaCO3·H2O and
ikaite Ikaite is the mineral name for the hexahydrate of calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone ...
CaCO3·6H2O, may precipitate from water at ambient conditions and persist as metastable phases.


With varying pH, temperature and salinity: CaCO3 scaling in swimming pools

In contrast to the open equilibrium scenario above, many swimming pools are managed by addition of sodium bicarbonate (NaHCO3) to about 2 mM as a buffer, then control of pH through use of HCl, NaHSO4, Na2CO3, NaOH or chlorine formulations that are acidic or basic. In this situation, dissolved inorganic carbon (total inorganic carbon) is far from equilibrium with atmospheric CO2. Progress towards equilibrium through outgassing of CO2 is slowed by In this situation, the dissociation constants for the much faster reactions :H2CO3 H+ + 2 H+ + allow the prediction of concentrations of each dissolved inorganic carbon species in solution, from the added concentration of (which constitutes more than 90% of Bjerrum plot species from pH 7 to pH 8 at 25 °C in fresh water). Addition of will increase concentration at any pH. Rearranging the equations given above, we can see that [Ca2+] = , and [] = . Therefore, when concentration is known, the maximum concentration of Ca2+ ions before scaling through CaCO3 precipitation can be predicted from the formula: :[\ce]_\max = \frac \times \frac The solubility product for CaCO3 (''K''sp) and the dissociation constants for the dissolved inorganic carbon species (including ''K''a2) are all substantially affected by temperature and salinity, with the overall effect that [Ca2+]max increases from freshwater to saltwater, and decreases with rising temperature, pH, or added bicarbonate level, as illustrated in the accompanying graphs. The trends are illustrative for pool management, but whether scaling occurs also depends on other factors including interactions with magnesium, Mg2+, Tetrahydroxyborate, and other ions in the pool, as well as supersaturation effects. Scaling is commonly observed in electrolytic chlorine generators, where there is a high pH near the cathode surface and scale deposition further increases temperature. This is one reason that some pool operators prefer borate over bicarbonate as the primary pH buffer, and avoid the use of pool chemicals containing calcium.


Solubility in a strong or weak acid solution

Solutions of strong acid, strong (hydrochloric acid, HCl), moderately strong (sulfamic acid, sulfamic) or weak acid, weak (acetic acid, acetic, citric acid, citric, sorbic acid, sorbic, lactic acid, lactic, phosphoric acid, phosphoric) acids are commercially available. They are commonly used as descaling agents to remove
limescale Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of old ...
deposits. The maximum amount of CaCO3 that can be "dissolved" by one liter of an acid solution can be calculated using the above equilibrium equations. * In the case of a strong monoacid with decreasing acid concentration [A] = [A], we obtain (with CaCO3 molar mass = 100 g/mol): :: :where the initial state is the acid solution with no Ca2+ (not taking into account possible CO2 dissolution) and the final state is the solution with saturated Ca2+. For strong acid concentrations, all species have a negligible concentration in the final state with respect to Ca2+ and A so that the neutrality equation reduces approximately to 2[Ca2+] = [A] yielding . When the concentration decreases, [] becomes non-negligible so that the preceding expression is no longer valid. For vanishing acid concentrations, one can recover the final pH and the solubility of CaCO3 in pure water. * In the case of a weak monoacid (here we take acetic acid with pKa, p''K''a = 4.76) with decreasing total acid concentration , we obtain: :: :For the same total acid concentration, the initial pH of the weak acid is less acid than the one of the strong acid; however, the maximum amount of CaCO3 which can be dissolved is approximately the same. This is because in the final state, the pH is larger than the p''K''a, so that the weak acid is almost completely dissociated, yielding in the end as many H+ ions as the strong acid to "dissolve" the calcium carbonate. * The calculation in the case of phosphoric acid (which is the most widely used for domestic applications) is more complicated since the concentrations of the four dissociation states corresponding to this acid must be calculated together with [], [], [Ca2+], [H+] and [OH]. The system may be reduced to a seventh degree equation for [H+] the numerical solution of which gives :: :where [A] = [H3PO4] + [] + [] + [] is the total acid concentration. Thus phosphoric acid is more efficient than a monoacid since at the final almost neutral pH, the second dissociated state concentration [] is not negligible (see phosphoric acid#pH and composition of a phosphoric acid aqueous solution, phosphoric acid).


See also

* Cuttlebone * Cuttlefish * Gesso * Limescale * Marble * Ocean acidification * Whiting event * List of climate engineering topics * Lysocline


References


External links

* * * ATC codes: and
The British Calcium Carbonate Association – What is calcium carbonate


{{DEFAULTSORT:Calcium Carbonate Calcium compounds Carbonates Limestone Phosphate binders Excipients Antacids Food stabilizers E-number additives