Calcite

calcite

wollastonite

tilleyite

laumontite

Images

Formula: CaCO₃
Carbonate, calcite group, trigonal paramorph of hexagonal vaterite and orthorhombic aragonite
Crystal System: Trigonal
Specific gravity: 2.7102 measured, 2.711 calculated
Hardness: 3
Streak: White
Colour: Colourless, white, yellow, red, orange, blue, green, pink, purple
Solubility: Readily soluble in hydrochloric, sulphuric and nitric acid
Common impurities: Mn,Fe,Zn,Co,Ba,Sr,Pb,Mg,Cu,Al,Ni,V,Cr,Mo
Environments:

Pegmatites
Carbonatites (essential)
Sedimentary environments (typical)
Metamorphic environments
Hydrothermal environments
Basaltic cavities

Calcite is a common and widespread mineral. It occurs in limestone, marble and chalk, in all of which it is essentially the only mineral present. It is an important constituent of calcareous marl and calcareous sandstone. Water carrying calcium carbonate in solution and evaporating in limestone caves often deposits calcite as stalagtites, stalagmites and incrustations. Both hot and cold calcium-bearing spring water may form around the mouths of the springs cellular deposits of calcite in the form of limestone, known as travertine (formed by hot mineral springs) or tufa (formed when carbonate minerals precipitate out of ambient temperature water). Calcite occurs as a primary mineral in some igneous rocks such as nepheline syenite, carbonatites and pegmatites. It is a late crystallisation product in cavities in lavas, and it is also a common mineral in the oxidation zone of hypothermal (high temperature), mesothermal (moderate temperature) and epithermal (low temperature) hydrothermal veins associated with sulphide ores.
Carbonates such as calcite are essential constituents of kimberlite.
Calcite is an essential constituent of limestone, marl and skarn.
It is a common but not essential constituent of sandstone.
It also may be found in dolostone.

Calcite may occur in all metamorphic facies with the exception of the very high-grade eclogite facies.

Selected Localities

The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. Calcite is a primary carbonate that occurs as interstitial material in magnetite ore and in veins. At the Three Mile deposit it occurs in marble with chlorite and talc. At the Two Mile deposit red fluorescing calcite occurs as coatings on magnetite (AJM 22.1.38).

At Bundoora, inner Melbourne, Victoria, Australia, ferroan calcite occurs in cavities in basalt as orange balls and bow-ties (AJM 20.1.33-37).

At the Hohe Tauern mountains, Salzburg, Austria, magnesite pseudomorphs after calcite have been found (KL p156).

At Irai, Brazil, quartz pseudomorphs after calcite have been found (KL p247).

At Yellow lake, near Ollala, British Columbia, Canada, brewsterite casts after calcite (pseudomorphs) have been found (KL p268).
White to creamy off-white calcite is found as complex rounded crystals perched on zeolites, especially brewsterite. Yellowish calcite is abundantly found as infillings of zeolite-lined vesicles, larger vugs and fracture seams (R&M 96.6.520).

At the Faraday mine, Faraday Township, Hastings county, Ontario, Canada, spectacular specimens of slender scalenohedral calcite occur, coated with hematite and botryoidal goethite (Canadian Museum of Nature specimen, R&M 94.5.410).

At lots 10 and 11 of concession 1, Bathurst Township, Lanark County, Ontario, Canada (DeWitts corner), the deposit is located in the Grenville Geological Province, which consists mostly of marble, gneiss, and quartzite. Syenite-migmatite was also reported in the area where the vein-dikes are located. Characteristic features of the vein-dikes include the fact that perfectly formed euhedral crystals of different minerals can often be found floating in calcite with no points of contact with the walls. Sometimes these crystals have inclusions of calcite, irregular or rounded in shape. It has been argued that at least some of the vein-dikes were formed as a result of melting of Grenville marble.
Calcite is the most abundant constituent of the vein-dikes. It forms local aggregates of salmon-pink, yellow or grey masses. The best-formed small spinel crystals, less than 10-mm in size, have been found in the salmon-pink calcite, whereas the best larger spinel crystals and the best pseudomorphs of corundum after spinel appear to occur in grey calcite toward the centre of the vein-dikes (R&M 97.6.556-564).

At the Thunder Bay Amethyst Mine, Thunder Bay District, Ontario, Canada, calcite has been found with sulphide inclusions (R&M 94.4.331-332).

At the Xiling Mine, Gongcheng County, Guilin, Guangxi, China, calcite occurs as white or greyish transparent to translucent crystals of an almost nailhead shape, up to several cm across. It has also been found as an aggregate of creamish white crystals, most of which are a cm or so in size, on a dark grey and surprisingly heavy matrix. There is also a dusting of pyrite on the back of the specimen (AESS).
Calcite from the Xiling Mine - Image

At Daye County, Huangshi, Hubei, China, fine large scalenohedral crystals of calcite are found, often coloured orange by inclusions of hematite, and sometimes coated with golden coloured chalcopyrite (AESS).
Calcite from Daye County - Image

At the Leiping Mine, Leiping, Guiyang County, Chenzhou, Hunan, China, attractive specimens have been found featuring spiky, vitreous, scalenohedral calcite crystals, sometimes coloured red-orange by hematite inclusions (AESS).
Calcite from Leiping - Image

At the Chashan Mine, Xianghualing Sn-polymetallic ore field, Linwu County, Chenzhou, Hunan, China, pure white, pearly calcite has been found that fluoresces pink under long wave UV (AESS).
Calcite from Chashan - Image

At the Xianghuapu Mine, Xianghualing Sn-polymetallic ore field, Linwu County, Chenzhou, Hunan, China, calcite twins have been found, some as much as 11 cm across (AESS).
Calcite from Xianghuapu - Image

At the Yaogangxian Mine, Yaogangxian W-Sn ore field, Yizhang County, Chenzhou, Hunan, China, white calcite, that fluoresces bright pink under long wave UV, occurs, sometimes as pagoda-like stacks of flattened nail-head crystals (AESS).
Calcite from Yaogangxian - Image

At the Shangbao Mine, Leiyang County, Hengyang, Hunan, China, pale yellow, sub-vitreous crystals of calcite, up to 13 cm long, have been found (AESS).
Calcite from Shangbao - Image

At the Pioneer quarry, Kwun Tong District, Kowloon, Hong Kong, China, the contact between granite and tuff is very sharp, and many veins and stringers of aplite and pegmatite from the batholith invade the country rock. The granite near the contact contains crystals of fluorite, pyrite, molybdenite and quartz, and calcite-filled vugs. Calcite also occurs along joint planes (Geological Society of Hong Kong Newsletter 1.7.6).

The Ma On Shan Mine, Ma On Shan, Sha Tin District, New Territories, Hong Kong, China, is an abandoned iron mine, with both underground and open cast workings. The iron ores contain magnetite as the ore mineral and occur predominantly as masses of all sizes enclosed in a large skarn body formed by contact metasomatism of dolomitic limestone at the margins of a granite intrusion. In parts of the underground workings magnetite is also found in marble in contact with the granite. The skarn rocks consist mainly of tremolite, actinolite, diopside and garnet. Calcite occurs in veins or vugs in the skarn zone, associated with fluorite, quartz, pyrite or serpentine (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

The Lin Fa Shan deposit, Tsuen Wan District, New Territories, Hong Kong, China, is located in a remote area of the Tai Mo Shan Country Park, on a steep west facing slope of Lin Fa Shan, just above the abandoned village of Sheung Tong. The surrounding hillsides are covered with shallow excavations, representing past searches for wolframite, the natural ore of tungsten. The abandoned workings are extremely dangerous with unsupported tunnels, open shafts and no maintenance since their closures in 1957; the workings should not be entered (http://industrialhistoryhk.org/lin-shan).
Lamellar calcite occurs in veins in the tungsten mine associated with fluorite, quartz and pyrite (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council).

At Yonghe, Liuyang County, Hunan Province, China, curious "chrysanthemum stones" have been found. These are ornamental stones displaying chrysanthemum-like patterns in a contrasting matrix. The composition of chrysanthemum stone is variable. Material from the "classic" occurrence at Yonghe consists of celestine, but specimens recovered from outcrops of the same strata at other places in the area are mostly mixtures of calcite, chalcedony and minor dolomite which replaced earlier celestine (Mindat).
Chrysanthemum Stone from Yonghe - Image

The Bairendaba Ag-polymetallic deposit, Hexigten Banner, Chifeng City, Inner Mongolia, China, is a mesothermal magmatic-hydrothermal vein-type silver - lead - zinc deposit, hosted in Hercynian (about 419 to 299 million years ago) quartz diorite.
It is suggested that, with decreasing temperature, mineral compositions changed progressively from tungstate and oxide, to diatomic sulphide, to simple sulphide, to an antimony sulphosalt mineral, and finally to an antimonide.
Calcite has been found as flattened, white, rhombohedral crystals to over 2 cm, associated with and included by dark gray acicular crystals of boulangerite (Minrec 53.347-359).

At the Huanggang Fe-Sn deposit, Hexigten Banner, Chifeng City, Inner Mongolia, China, fine specimens of white or pink calcite have been found, that fluoresce fiery red under short wave or long wave UV, and strong pink under 405 nm radiation (AESS).
Calcite from Huanggang - Image

At the Shengou lead-zinc mine, Xide County, Liangshan Yi, Sichuan, China, calcite occurs as aggregates of coarse poorly formed pinkish white crystals (AESS)
Calcite from Shengou - Image

At Yiwu, Jinhua, Zhejiang, China, extraordinary "panda calcite" is found, comprising well formed hexagonal prisms with flat tops with a dark spot in the middle. The calcite is dull, whitish and translucent (AESS).
Calcite from Yiwu - Image

At the Tantara Mine, Shinkolobwe, Kambove Territory, Haut-Katanga, DR Congo, shattuckite pseudomorphs after calcite have been found with dioptase (KL p230).

At the Mashamba West Mine, Sicomines copper-cobalt project, Mutshatsha, Lualaba, DR Congo, Two specimens of hot-pink cobalt-rich calcite, both about 10 cm across, have been found that exhibit shallow vugs in which very bright, very thin wires of copper lie lightly on the pink calcite linings. Also pink cobalt-rich calcite occurs here with green malachite Minrec 55.1.86-88).

At Canaveille, Pyrenees, France, posnjakite and langite pseudomorphs after calcite have been found (KL p193).

At Idar-Oberstein, Birkenfeld, Rhineland-Palatinate, Germany, quartz pseudomorphs after calcite have been found (R&M 95.3.275).

At Jalgaon, Maharashtra province, India, chalcedony pseudomorphs after calcite on chalcedony have been found (KL p255).

At Agrigento, Sicily, Italy, calcite pseudomorphs after aragonite have been found, with sulphur (KL p151).

At the Santa Eulalia Mining District, Aquiles Serdán Municipality, Chihuahua, Mexico, calcite pseudomorphs after baryte have been found (KL p152).

At Charcas, Charcas Municipality, San Luis Potosí, Mexico, the primary minerals are sphalerite, galena, chalcopyrite, bornite, tetrahedrite, arsenopyrite, pyrite and silver minerals such as jalpaite, diaphorite and acanthite. In the host rock, as metamorphic or alteration minerals, danburite, datolite, hedenbergite, epidote, chlorite, andradite, actinolite and wollastonite have been reported.
Quartz, calcite and danburite crystallised during the entire life of the systems, throughout the intrusive emplacement, metamorphism, and mineralising events. With depth, both sphalerite and galena decrease while chalcopyrite increases.
Secondary sulphides formed include bornite, covellite, digenite and chalcocite. Native silver, native gold, hematite and goethite were deposited after the sulphides (Minrec 55.6.727-728).
Calcite specimens have come from every mine in the district. Crystals are typically fluorescent red to pink, and more rarely blue and green, under ultraviolet light. The best-known calcite habit is the tabular hexagonal “poker chip” crystals. Specimens range from attractive, staggered, stacked tablets to single huge discs 25 cm across with a thickness of 5 cm.
In early 2009, groups of lustrous golden discs forming elegant hemispheres emerged from the San Bartolo mine. The spheres are up to 10 cm across with discs to 3 cm. On one side of the blades, the tips are coated with goethite creating a colour contrast with the calcite.
Calcite from the San Bartolo Mine - Image
Late in 2010, calcite scepters were discovered in the San Bartolo mine, with white calcite forming the head of the scepter emerging from a pale beige-coloured rod. Most of the specimens are in the 4 to 5 cm range, with a few reaching 11 cm.
In 2016 lustrous, transparent, colourless, doubly terminated hexagonal prismatic crystals of calcite to 2 cm were discovered resting on plates of drusy cream-yellow calcite. The specimens reach 12 cm across.
In 2022, spectacular, transparent, colourless, very elongated and twinned, prismatic, faden-like calcite crystals, doubly terminated and measuring up to 25 cm long and 5 cm wide, were found at the Rey y Reina mine. These are floaters and rarely show contact or attach points. Some have small chalcopyrite and sphalerite crystals attached.
Calcite from the Rey y Reina Mine - Image
Also in 2022, large, lustrous, flat calcite prisms with thin pyrite coatings were found at the old Las Eulalias mine.
Calcite is seen in association with an extensive number of minerals, including datolite, danburite and quartz. Calcite is commonly replaced by quartz, and in a few cases by danburite. Some quartz epimorphs (perimorphs) have retained the morphology of the original calcite crystal but the cores are empty. In other cases, calcite has replaced other minerals such as danburite, traces of which may remain in the cores (Minrec 55.6.727-37-743).

At the Tsumeb mine, Namibia, mottramite pseudomorphs after calcite have been found (KL p202).
Calcite from Tsumeb - Image

At the Olenitsa River, White Sea Coast, Karelia Republic, Russia, calcite pseudomorphs after ikaite have been found; these pseudomorphs are called glendonites. Ikaite is formed at sub-zero temperatures and at room temperature it rapidly dehydrates to calcite, and the glendonites so formed are exceedingly fragile and collapse easily to a white powder (R&M 97.6.496-509).

At Dalnegorsk, Primorsky Krai, Russia, calcite pseudomorphs after fluorite have been found, with a quartz coating (KL p153).

At Calvinia, near Capetown, Cape Province, South Africa, prehnite pseudomorphs after calcite have been found (KL p240).

At the Mariquita Mine (Sultana Mine), Usagre, Badajoz, Extremadura, Spain, calcite is the most common gangue mineral formed during the last phase of mineralisation, deposited in the space between the primary orebody and the host rock. In cavities it forms prismatic crystals to 1 cm in size, mainly associated with calomel and eglestonite, with minor primary sulphides, rosasite (inclusions of which may stain the calcite crystals blue) and hematite. While growing, some calcite crystals also trapped mercury oxychlorides (especially terlinguaite) and edgarbaileyite. Calcite has also been found as sharp, colourless ladder-shaped aggregates a few millimeters long, associated with calomel, eglestonite, corderoite and native mercury (MinRec 55.4.490-491).
Calcite from the Mariquita Mine - Image

At Asar hill, Güğtı, Dursunbey district, Balikesir province, Marmara region, Turkey, quartz pseudomorphs after calcite have been found (KL p248).

From Wheal Wrey, Wrey and Ludcott United Mines, St Ive, Cornwall, England, UK, specimen BM.1964,R5426 from the Natural History Museum, London, features colourless, translucent, blocky prismatic crystals of calcite, sprinkled with cubic microcrystals of pyrite (RES2 p147).

In a cavity at the Smallcleugh Mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, calcite is the last mineral to form. it occurs rarely as crusts of minute nailhead crystals, which often have a mammillary form (JRS 18.20-21).
The calcite often, but not always, fluoresces pink under long wave UV and red under short wave. It has been found with sphalerite, quartz, pyrite and brianyoungite (AESS).

At the Calton Hill quarry, Buxton, Derbyshire, England, UK, calcite crystals have been found coloured red by iron oxide, on quartz associated with minor goethite (RES p115, 116).

At the Odin mine, Castleton, Derbyshire, England, UK, calcite crystals have been found on dark purple fluorite (RES p129).

At Millclose mine, Darley Dale, Derbyshire, England, UK, calcite crystals have been found on a matrix of sphalerite and fluorite, some with minor pyrite and chalcopyrite (RES p95).

At Eyam, Derbyshire, England, UK, calcite is associated with sphalerite, fluorite and galena (RES p117).

At Ladywash mine, Eyam, Derbyshire, England, UK, calcite crystals have been found with a dusting of minute pyrite crystals, and calcite occurs on a fluorite - limestone matrix (RES p119, 120).

At the Riber mine, Matlock, Derbyshire, England, UK, calcite has been found with inclusions of chalcopyrite, malachite and copper, with occasional pyrite and rarely bornite (RES p68).

At the Magpie mine, Sheldon, Derbyshire, England, UK, calcite crystals have been found with a dusting of minute pyrite crystals (RES p115).

At the Hampstead Farm quarry, Chipping Sodbury, Gloucestershire, England, calcite crystals dusted with pyrite have been found, also calcite on pyrite overgrowing baryte, and calcite on marcasite coating baryte (RES p172, 173).

At Croft quarry, Blaby, Leicestershire, England, UK, several generations of calcite have been identified. It has been found with minor analcime on altered tonalite matrix. Pseudomorphs of calcite after laumontite have been found here, sometimes associated with later crystals of analcime (RES p186-190, R&M 20.9-12).

At Enderby Warren Quarry, Enderby, Blaby, Leicestershire, England, UK, calcite occurs in quartz-diorite and tonalite associated with palygorskite and dolomite (R&M 20.13).

At Granitethorpe quarry, Sapcote, Blaby, Leicestershire, England, UK, joint-planes in the diorite were sometimes coated with green-stained calcite or opal and some of the joints were slickensided and contained a film of calcite (JRS 20.13).

At Lane's Hill quarry, Stoney Stanton, Blaby, Leicestershire, England, UK, a specimen has been found which showed three generations of Fe-bearing dolomite followed by calcite deposition (JRS 20.13).

At the Church Gresley opencast coal mine, Ashby-de-la-Zouch, Northwest Leicestershire, Leicestershire, England, calcite occurs in septarian nodules (RES p226, 227).

At Breedon quarry, Breedon on the Hill, Northwest Leicestershire, Leicestershire, England, UK, iron-stained calcite crystals have been found covered with small acicular crystals of malachite (RES p203).

At Cloud Hill quarry, Breedon on the Hill, Northwest Leicestershire, Leicestershite, England, UK, calcite has been found with inclusions of chalcopyrite. Also a specimen has been found with minor attached dolomite (RES p205, 208).

At Lord Ferrises mine, Staunton Harold, Northwest Leicestershire, Leicestershire, calcite occurs with galena, baryte, sphalerite and chalcopyrite on dolomitised limestone (RES p218 to 223).

At Barrasford Quarry, Chollerton, Northumberland, England, UK, small amounts of calcite in have been found in vesicles associated with both datolite and pectolite (JRS 21.7-7).

At Wotherton mine, Chirbury, Shropshire, England, UK, calcite occurs with chalcopyrite, pyrite and baryte (RES p285, 286).

At Snailbeach mine, near Minsterley, Shropshire, England, UK, calcite occurs with sphalerite and also with harmotome, quartz, chalcopyrite or galena (RES p270 to 275).

At Llynclys quarry, near Oswestry, Shropshire, England, UK, calcite occurs with dolomite (RES p294).

At Tankerville mine, Worthen, Shropshire, England, UK, calcite occurs with galena (RES p281).

At Cauldron Low quarry, Staffordshire, England, UK, calcite occurs with galena and sphalerite on limestone (RES p313).

At the Ecton mine, Staffordshire, England, UK, calcite occurs with chalcopyrite (RES p305 to 307).

At Hartshill, Nuneaton, Warwickshire, England, UK, manganoan calcite has been found with manganite (RES p321).

At Judkins quarry, Nuneaton, Warwickshire, England, UK, calcite has been found with baryte (RES p323).

At Glen Brittle, Minginish, Isle of Skye, Eilean á Chèo, Highland, Scotland, UK, vesicles are abundant in basaltic lava, mostly filled with mordenite-quartz intergrowths, but some are devoid of mordenite. A central filling of white calcite, seen as rhombic cleavage surfaces up to 150 mm across, is present in a small number of the mordenite-filled vesicles, and similar coarsely crystalline calcite is a conspicuous constituent of the filling of the vesicles that are devoid of mordenite, but contain prehnite (JRS 23.86-90).

The Nelly James Mine, Miller Canyon, Miller Peak, Cochise County, Arizona, USA, is a former small surface lead, copper, zinc, gold and silver mine located at an altitude of 7250 feet. Mineralisation is a vein deposit Mindat). The mine is now famous for fluorescent minerals collected from the dumps, including calcite (fluoresces red), hydrozincite (sky blue), powellite (creamy-yellow), smithsonite (crimson red), sphalerite (yellow-orange) and willemite (green).
Calcite is one of the most common minerals at the mine and is dominantly associated with willemite. The calcite is typically massive and white in daylight, turning tan or brown where the contained manganese has oxidised. Under shortwave UV light the fluorescent response is usually a bright orange-red, but pinkish-red is also present. In some specimens the calcite fluoresces a deeper red colour. Secondary crosscutting veinlets of calcite may fluoresce a different shade of red than the massive primary calcite. Under longwave UV light the response is a weaker pink to pale red colour. Under medium range UV light the response is a weak red colour. The calcite also exhibits a very brief sustained luminescence (phosphorescence) upon removal of the shortwave UV source (R&M 97.1.48-56).

At the Camp Verde district, Yavapai county, Arizona, USA, calcite pseudomorphs after glauberite have been found (KL p155, R&M 87.1.18).

At the Copper Falls Mine, Copper Falls, Keweenaw county, Michigan, USA, mineralisation occurs primarily in hydrothermal veins cutting preexisting lavas and as amygdules in the Ashbed flow.
Copper Falls has produced some exceptional calcite crystals. Copper inclusions in calcite were noted as early as 1850. Perhaps the finest is a gem-quality calcite crystal resting on a matrix of native copper which is now housed at the A E Seaman Mineral Museum (MinRec 54.1.95-105).

The Central Mine, Central, Keweenaw county, Michigan, USA, initially targeted a series of sub-parallel mineralised fissure veins where the most copper-rich portion of the vein was close to the base of the main greenstone flow.
The Central mine has produced some outstanding crystallised calcite specimens, including beautifully transparent and morphologically complex calcite crystals coloured by minute inclusions of native copper. Another unique style of calcite specimen found here shows gemmy crystals, typically scalenohedral, with dark red to brown hematite inclusions forming phantoms (MinRec 54.1.53-81).

The Cliff Mine, Phoenix, Keweenaw county, Michigan, USA, is situated at the base of a roughly 70-metre basalt cliff. A curious feature of the impressive thickness of the greenstone flow here is that it contains zones of “pegmatoid”: areas where slow cooling in the core of the lava flow allowed for large feldspar crystals exceeding 1 cm to grow. Such features are normally only observed in intrusive igneous rocks and are almost unheard of in basalt flows.
The Cliff mine primarily exploited rich copper mineralisation in the Cliff fissure (vein). Although mineralised with copper to some extent along its entire length, the part of the vein just below the greenstone flow carried the richest copper mineralisation by far. A significant amount of the copper recovered at the Cliff mine came from amygdaloids in the tops of 13 basalt flows which were cut by the Cliff vein. The discovery and mining of this vein proved that the veins were the source of the large masses of float copper that were already well known, and proved that the primary ore mineral in the district was native copper, not sulphides, as had been suspected earlier.
Calcite is a common vein-filling mineral as massive white material with prominent rhombohedral cleavage. Crystals occurring in vugs are scalenohedral, less commonly rhombohedral. Calcite crystals are sometimes white and opaque, but are more commonly colourless or pale yellow and transparent. Copper inclusions in calcite are not uncommon, but the Cliff mine is not a particularly important locality for Michigan’s highly sought-after copper-in-calcite specimens (MinRec 54.1.25-49).

At Joplin, Missouri, USA, hemimorphite pseudomorphs after calcite have been found (KL p225).

At Cookes Peak mining district, Luna county, New Mexico, USA, calcite is associated with aragonite in cave-like formations, and it is also very common in cavities with ore minerals and fluorite (R&M 94.3.226).

At the Empire State No. 4 Mine, Balmat, Balmat-Edwards Zinc Mining District, St. Lawrence County, New York, USA, large crystals of pink calcite have been found (MinRec 55.3.355-356).
Calcite from the Empire State No 4 Mine - Image

At The Dafoe Property, Pierrepont, St Lawrence county, New York, USA, calcite is associated with late stage quartz, allanite-(Ce) and occasionally hematite (R&M 94.5.452-455).

At the Purple Diopside Mound, Rose Road, Pitcairn, St. Lawrence county, New York, USA, calcite, as a secondary coating on various minerals, fluoresces a greenish white under both long wave and short wave UV. The calcite in marble is not fluorescent (R&M 97.5.442).

At the Suever Stone Company quarry, Delphos, Van Wert county, Ohio, USA, calcite occurred as crystals and pocket fillings. Multiple forms of calcite were encountered, including the rhombohedron, scalenohedral (dogtooth) crystals and blunt tapered crystals. The rhombohedra are frequently truncated by the pinacoid {001}. This is rare for calcite occurrences in Ohio in general, but it is typical of crystals from other oil-saturated strata in the state. Some of the calcite is quite fluorescent under longwave ultraviolet light; deposits of this calcite seem to be late-stage coatings, sometimes on surfaces of existing calcite crystals; levels of fluorescence range from pink to brilliant red. Earlier-formed calcite does not fluoresce (R&M 95.6.502-505). Some calcite from the lower level shows saddle-shaped junctions between crystals that are crystallographically continuous with the crystal they abut. Fluorite and pyrite also occur with similar unusual features. All of these unusual mineral examples have one thing in common; they were found in oil-saturated pockets. Petroleum is often seen trapped in calcite crystals, and its presence seems to be linked to the "saddles", but the mechanism for their formation is not known (R&M 95.6.512-514).

At the Mid-Continent mine, Picher, Oklahoma, USA, a gypsum pseudomorph after calcite has been found with melanterite on sphalerite (KL p189).

At the Luck Leesburg Plant, Leesburg, Loudoun county, Virginia, USA, calcite is ubiquitous and is most commonly seen as tiny white crystals scattered on apophyllite or prehnite (R&M 98.2.124-125).

Alteration

Calcite and aragonite are precipitated according to the following reactions:
Carbon dioxide in the atmosphere is dissolved in rainwater forming weak carbonic acid:
H₂O + CO₂ → H₂CO₃
Carbonic acid dissolves limestone forming calcium bicarbonate
H₂CO₃ + CaCO₃ → Ca(HCO₃)₂
This solution percolates into caves where calcium carbonate may be precipitated as calcite with the release of liquid water and gaseous carbon dioxide:
Ca(HCO₃)₂ ⇆ CaCO₃ (solid) + H₂O (liquid) + CO₂ (gas) (R&M 91-4:329)
The net effect of these changes could be written as the reversible reaction
CaCO₃ (solid) + H₂CO₃ (in solution) ⇌ Ca²⁺ + 2(HCO₃)^-
The forward reaction, solution of calcium carbonate, occurs in acid environments, and the reverse reaction, precipitation of calcium carbonate, occurs in strongly basic (alkaline) environments. (KB p62)

aegirine, epidote and CO₂ to albite, hematite, quartz, calcite and H₂O
4NaFe³⁺Si₂O₆ + 2Ca₂(Al₂Fe³⁺[Si₂O₇](SiO₄)O(OH) + 4CO₂ → 4Na(AlSi₃O₈) + 3Fe₂O₃ + 2SiO₂ + 4CaCO₃ + H₂O (DHZ 2A p511)

åkermanite and CO₂ to diopside and calcite
Ca₂MgSi₂O₇ + CO₂ ⇌ CaMgSi₂O₆ + CaCO₃
The maximum stability limit of åkermanite in the presence of excess CO₂ is about 6 kbar. Below that pressure, at relatively lower temperatures, åkermanite reacts with CO₂ to form diopside and calcite according to the reaction: (JVW p144)

albite, chlorite and calcite to Ca, Mg-rich jadeite, Al-rich glaucophane, quartz, CO₂ and H₂O
8Na(AlSi₃O₈) + (Mg_4.0Fe_2.0)(AlSi₃O₁₀)(OH)₈ + CaCO₃ → 5(Na_0.8Ca_0.2)(Mg_0.2Al_0.8Si₂)₆ + 2Na₂(Mg₃Al₂)(Al_0.5Si_7.5)O₂₂(OH)₂ + 2SiO₂ + CO₂ + 2H₂O
In low to intermediate metamorphism jadeite-glaucophane assemblages may arise from reactions such as the one above. (DHZ 2A p475)

calcium amphibole, calcite and quartz to diopside-hedenbergite, anorthite, CO₂ and H₂O
Ca₂(Mg,Fe²⁺)₃Al₄Si₆O₂₂(OH)₂ + 3CaCO₃ + 4SiO₂ = 3Ca(Fe,Mg)Si₂O₆ + 2Ca(Al₂Si₂O₈) + 3CO₂ + H₂O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction. (DHZ 2A p272)

amphibole, chlorite, paragonite, ilmenite, quartz and calcite to garnet, omphacite, rutile, H₂O and CO₂
NaCa₂(Fe₂Mg₃)(AlSi₇)O₂₂(OH)₂ + Mg₅Al(AlSi₃O₁₀)(OH)₈ + 3NaAl₂(Si₃Al)O₁₀(OH)₂ + 4Fe²⁺Ti⁴⁺O₃ + 9SiO₂ + 4CaCO₃ → 2(CaMg₂Fe₃)Al₄(SiO₄)₆ + 4NaCaMgAl(Si₂O₆)₂ + 4TiO₂ + 8H₂O + 4CO₂ In low-grade rocks relatively rich in calcite the garnet-omphacite association may be due to reactions such as the above. (DHZ 2A p453)

anorthite to calcite and kaolinite in the early Earth's atmosphere
CO₂ + H₂O + anorthite → calcite + kaolinite
CO₂ + 2H₂O + CaAl₂Si₂O₈ → CaCO₃ + Al₂Si₂O₅(OH)₄ (JVW p634)

anorthite, H₂O and CO₂ ⇌ kaolinite and calcite
2CaAl₂ Si₂O₈ + 4H₂O + 2CO₂ ⇌ Al₄Si₄O₁₀(OH)₈ + 2CaCO₃
Calcite is found as a low-temperature, late-stage alteraation product according to the above reaction. (DHZ 5B p128)

anorthite and calcite to meionite (scapolite series)
3Ca(Al₂Si₂O₈) + CaCO₃ ⇌ Ca₄Al₆O₂₄(CO₃)
This reaction occurs in the presence of a high CO₂ pressure in an environment deficient in (Al+Na+K). (DHZ 4 p331)

antigorite and calcite to forsterite, diopside, CO₂ and H₂O
3Mg₃Si₂O₅(OH)₄ + CaCO₃ → 4Mg₂SiO₄ + CaMgSi₂O₆ + CO₂ +6 H₂O
This reaction has been found to occur in antigorite schist at about 3 kbar pressure and 400 to 500^oC (greenschist facies). (DHZ 1A p263)

aragonite or calcite and Mg²⁺ (from Mg-rich fluid) to dolomite and Ca²⁺
2CaCO₃ + Mg²⁺ ⇌ CaMg(CO₃)₂ + Ca²⁺

augite and CO₂ to enstatite-ferrosilite, calcite and quartz
Ca(Mg,Fe)Si₂O₆ + CO₂ → (Mg,Fe)SiO₃ + CaCO₃ + SiO₂ (DHZ 2A p384)

bustamite, tephroite and calcite to glaucochroite and CO₂
CaMn²⁺Si₂O₆ + Mn²⁺₂(SiO₄) + 2CaCO₃ ⇌ 3CaMn²⁺(SiO₄) + 2CO₂ (DHZ 1A p348)

calcite, Ba²⁺, H₂S and O₂ to baryte, Ca²⁺, CO₂ and H₂O
CaCO₃ + Ba²⁺ + H₂S + 2O₂ = BaSO₄ + Ca²⁺ + CO₂ and H₂O
Baryte may be precipitated by the action of ore fluid and groundwater on calcite. (DHZ 5B p16)

calcite, Fe²⁺ and Mg²⁺ to ankerite and Ca²⁺
4CaCO₃ + Fe²⁺ + Mg²⁺ = 2Ca(Mg0.5Fe_0.5)(CO₃)₂+ 2Ca²⁺
Ankerite is believed to be formed from calcite hydrothermally according to the above reaction. (DHZ 5B p228)

calcite, hematite and quartz to andradite and CO₂
3CaCO₃ + Fe₂O₃ + 3SiO₂ → Ca₃Fe³⁺₂Si₃O₁₂ + 3CO₂

calcium amphibole, calcite and quartz to diopside-hedenbergite, anorthite, CO₂ and H₂O
Ca₂(Mg,Fe²⁺)₃Al₄Si₆O₂₂(OH)₂ + 3CaCO₃ + 4SiO₂ = 3Ca(Fe,Mg)Si₂O₆ + 2Ca(Al₂Si₂O₈) + 3CO₂ + H₂O
Diopside-hedenbergite occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies, where it may form according to the above reaction. (DHZ 2A p272)

dellaite and calcite to spurrite and H₂O
2Ca₆(Si₂O₇)(SiO₄)(OH)₂ + 3CaCO₃ ⇌ 3Ca₅(SiO₄)₂(CO₃) + 2H₂O
Higher temperatures favour the forward reaction (MM 34.1.1-16).

diopside, CO₂ and H₂O to tremolite, calcite and quartz
5CaMgSi₂O₆ + 3CO₂ + H₂O = Ca₂Mg₅Si₈O₂₂(OH)₂ + 3CaCO₃ + 2SiO₂
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with dolomite. (DHZ 2A p276)

diopside and dolomite to forsterite, calcite and CO₂
CaMgSi₂O₆ + 3CaMg(CO₃)₂ → 2Mg₂SiO₄ + 4CaCO₃ + 2CO₂
This is a high-grade metamorphic change occurring at temperature in excess of 600^oC. (MOM, DHZ 5B p213)

diopside, dolomite, CO₂ and H₂O to actinolite and calcite
4CaMgSi₂O₆ + CaMg(CO₃)₂ + CO₂ + H₂O = Ca₂Mg₅Si₈O₂₂(OH)₂ + 3CaCO₃
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with CO₂ and H₂O. (DHZ 2A p276)

diopside, dolomite and H₂O ⇌ hydroxylclinohumite, calcite and CO₂
2CaMgSi₂O₆ + 7CaMg(CO₃)₂ + H₂O ⇌ Mg₉(SiO₄)₄(OH)₂ + 9CaCO₃ + 5CO₂
In the nodular dolomites, clinohumite associated with calcite occurs in a narrow zone in the central parts of the nodules due to the above reaction (DHZ 1A p264).

diopside, forsterite and calcite to monticellite and CO₂
CaMgSi₂O₆ + Mg₂SiO₄ + 2CaCO₃ → 3CaMgSiO₄ + 2CO₂
This reaction requires a high temperature. (DHZ 2A p271)

diopside-hedenbergite and CO₂ to enstatite- ferrosilite, calcite and quartz
Ca(Mg,Fe)Si₂O₆ + CO₂ → (Mg,Fe²⁺)SiO₃ + CaCO₃ + SiO₂ (DHZ 2A p136)

dolomite and chert to talc and calcite
3CaMg(CO₃)₂ + 4SiO₂ + H₂O → Mg₃Si₄O₁₀(OH)₂ + 3CaCO₃ + 3CO₂
Metamorphism of siliceous carbonate rocks causes the formation of hydrous phases such as talc and tremolite. (DHZ 5B p127) This is a very low-grade metamorphic reaction occurring at temperature between about 150^oC and 250^oC. (MOM)

dolomite and muscovite to phlogopite, calcite, CO₂ and Al₂O₃
3CaMg(CO₃)₂ + KAl₂(AlSi₃O₁₀)(OH)₂ → KMg₃(AlSi₃O₁₀)(OH)₂ + 3CaCO₃ + 3CO₂ + Al₂O₃
The excess alumina may be used to form spinel (DHZ 3 p51)

dolomite, K-feldspar and H₂O to phlogopite, calcite and CO₂
3CaMg(CO₃)₂ + KAlSi₃O₈ + H₂O = KMg₃AlSi₃O₁₀(OH)₂ + 3CaCO₃ + 3CO₂
In the presence of Al and K the metamorphism of dolomite leads to the formation of phlogopite according to the above equation. (DHZ 5B p213)

dolomite and quartz to forsterite, calcite and CO₂
2CaMg(CO₃)₂ + SiO₂ → Mg₂SiO₄ + 2CaCO₃ + 2CO₂ In siliceous dolostone dolomite and quartz may react to form either diopside or forsterite, with diopside forming at a lower temperature than forsterite. (DHZ 2A p270, 1A p264)

dolomite, quartz and H₂O to tremolite, calcite and CO₂
5CaMg(CO₃)₂ + 8SiO₂ + H₂O → Ca₂Mg₅Si₈O₂₂(OH)₂ + 3CaCO₃ + 7CO₂
This is a metamorphic reaction in dolomitic limestone. (MOM p496)

dolomite and tremolite to forsterite, calcite, CO₂ and H₂O
Ca₂Mg₅Si₈O₂₂(OH)₂ + 11CaMg(CO₃)₂ → 8Mg₂SiO₄ + 13CaCO₃ + 9CO₂ + H₂O
Dolomite can be metamorphosed to talc and calcite, then at higher temperatures the talc and calcite react to form tremolite. In turn tremolite reacts with dolomite to form forsterite, according to the above equation.

(DHZ 5B p213) enstatite and calcite to forsterite, diopside and CO₂
3Mg₂Si₂O₆ + 2CaCO₃ ⇌ 2Mg₂SiO₄ + 2CaMgSi₂O₆ + 2CO₂
enstatite is uncommon in the more calcareous hornfels due to reactions such as the above. (DHZ 2A p135)

enstatite, calcite and quartz to diopside and CO₂
3Mg₂Si₂O₆ + 2CaCO₃ + 2SiO₂ ⇌ + 2CaMgSi₂O₆ + 2CO₂ enstatite is uncommon in the more calcareous hornfels due to reactions such as the above. (DHZ 2A p135)

ferro-actinolite, calcite and quartz to hedenbergite, CO₂ and H₂O
Ca₂Fe²⁺₅Si₈O₂₂(OH)₂ + 3CaCO₃ + 2SiO₂ ⇌ 5CaFe²⁺Si₂O₆ + 3CO₂ + H₂O In some calc-silicate rocks hedenbergite is the product of metamorphism of iron-rich sediments, according to the above reaction, probably due to the instability of ferro-actinolite with rising temperature. (DHZ 2A.273)

forsterite, calcite and quartz to diopside and CO₂
Mg₂SiO₄ + 2CaCO₃ + 3SiO₂ → 2CaMgSi₂O₆ + 2CO₂
In high temperature environments with excess SiO₂ diopside may form accoring to the above reaction. (DHZ 2A.271)

forsterite, calcite and quartz to monticellite and CO₂
Mg₂SiO₄ + 2CaCO₃ + SiO₂ → 2CaMg(SiO₄) + 2CO₂

forsterite, diopside and calcite to monticellite and CO₂
Mg₂SiO₄ + CaMgSi₂O₆ + 2 CaCO₃ ⇌ 3CaMg(SiO₄) + 2 CO₂
This reaction occurs during contact metamorphism of magnesian limestone. (DHZ 1A p353)

forsterite and dolomite to calcite and hydroxylclinohumite
4Mg₂SiO₄ + CaMg(CO₃)₂ + H₂O → Mg₉(SiO₄)₄(OH)₂ + CaCO₃ + CO₂
This is probably the reaction responsible for a forsterite- clinohumite assemblage in silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA (DHZ 1A p264).

forsterite, dolomite and H₂O to calcite, hydroxylclinohumite and CO₂
4Mg₂SiO₄ + CaMg(CO₃)₂ + H₂O → Mg₉(SiO₄)₄(OH)₂ +CaCO₃ + CO₂
A forsterite-clinohumite assemblage in the silica-rich dolomite in the aureole of the Alta granodiorite in Utah, USA, is probably due to the above reaction. (DHZ 1A.264)

grossular, diopside, monticellite, calcite and H₂O to vesuvianite, quartz and CO₂
10Ca₃Al₂(SiO₄)₃ + 3CaMgSi₂O₆ + 3CaMg(SiO₄) + 2CaCO₃ + 8H₂O ⇌ 2Ca₁₉Al₁₀Mg₃(SiO₄)₁₀ (Si₂O₂)₄O₂(OH)₈ + 3SiO₂ + 2CO₂ A common association in calc-silicate metamorphism can be represented by the above equation. Vesuvianite stability will tend to increase with increasing water and decrease as the activity of CO₂ rises. (DHZ 1A.714)

hematite, wüstite, quartz and calcite to andradite, hedenbergite magnetite and CO₂
2Fe₂O₃ + 2FeO + 5SiO₂ + 4CaCO₃ → Ca₃Fe³⁺₂(SiO₄)₃ + CaFe²⁺Si₂O₆ +Fe²⁺Fe³⁺₂O₄ +4CO₂

hornblende, calcite and quartz to Fe-rich diopside, anorthite, CO₂ and H₂O
Ca₂(Mg,Fe²⁺)₃(Al₄Si₆)O₂₂(OH)₂ + 3CaCO₃ + 4SiO₂ = 3Ca(Mg,Fe²⁺)Si₂O₆ + 2Ca(Al₂Si₂O₈) + 3CO₂ + H₂O
Fe-rich diopside occurs commonly in regionally metamorphosed calcium-rich sediments and basic igneous rocks belonging to the higher grades of the amphibolite facies. The above reaction is typical. (DHZ 2A.272)

kaolinite, dolomite, quartz and H₂O to chlorite, calcite and CO₂
Al₂Si₂O₅(OH)₄ + 5CaMg(CO₃)₂ + SiO₂ + 2H₂O ⇌ Mg₅Al(AlSi₃O₁₀)(OH)₈ + 5CaCO₃ + 5CO₂
Chlorite often forms in this way from reactions between clay minerals such as kaolinite and carbonates such as dolomite. (KB p377)

laumontite and calcite to prehnite, quartz, H₂O and CO₂
CaAl₂Si₄O₁₂.4H₂O + CaCO₃ → Ca₂Al(Si₃Al)O₁₀(OH)₂ + SiO₂ + 3H₂O + CO₂
Prehnite and pumpellyite form from the Ca zeolites in the presence of calcite, as in the above equation. (DHZ 5B.127)

meionite (scapolite series) and augite to garnet, calcite and quartz
Ca₄Al₆O₂₄(CO₃) + 3Ca(Mg,Fe²⁺)Si₂O₆ ⇌ 3Ca₂(Mg,Fe²⁺)Al₂(SiO₄)₃ + CaCO₃ + 3SiO₂ (DHZ 4.334)

meionite (scapolite series), calcite and quartz to grossular and CO₂
Ca₄Al₆O₂₄(CO₃) + 5CaCO₃ + 3SiO₂ ⇌ 3Ca₃Al₂(SiO₄)₃ + 6CO₂ (DHZ 4.334)

monticellite and CO₂ to åkermanite, forsterite and calcite
3CaMgSiO₄ + CO₂ ⇌ Ca₂MgSi₂₇ + Mg₂O₇ + CaCO₃
At 4.3 kbar pressure the equilibrium temperature is about 890^oC (granulite facies). (DHZ 1A.357)

monticellite and spurrite to merwinite and calcite
2CaMg(SiO₄) + Ca₅(SiO₄)₂(CO₃) ⇌ 2Ca₃Mg(SiO₄)₂ + CaCO₃

phlogopite, calcite and silica to diopside, K-feldspar, H₂O and CO₂
KMg₃(AlSi₃O₁₀)(OH)₂ + 3CaCO₃ + 6SiO₂ = 3CaMgSi₂O₆ + K(AlSi₃O₈) + H₂O + 3CO₂
In reaction zones between interbedded carbonate and pelitic beds of the calc-mica schist, phlogopite may alter according to the above reaction. (DHZ 2A.272)
The association of phlogopite and calcite is stable only in the absence of excess silica. (DHZ 3.51)

quartz and calcite to wollastonite and CO₂
3SiO₂ + 3CaCO₃ ⇌ Ca₃Si₃O₉ + 3CO₂ (gaseous)
This is a contact metamorphic change occurring at temperatures from about 600°C such as in the immediate border zone of an igneous intrusion into limestone. (MOM p486, KB p417) High pressure inhibits the forward reaction by suppressing the formation of gaseous CO₂. (KB p18) At 10 kbar pressure the equilibrium temperature is about 1,070^oC (granulite facies). (SERC)

talc and calcite to dolomite and quartz
talc + calcite + CO₂ ⇌ dolomite + quartz + H₂O
Mg₃Si₄O₁₀(OH)₂ + 3CaCO₃ + 3CO₂ ⇌ 3CaMg(CO₃)₂ + 4SiO₂ + H₂O

(JVW p144) talc and calcite to tremolite dolomite, CO₂ and H₂O
2Mg₃Si₄O₁₀(OH)₂ + 3CaCO₃ +4SiO₂ → Ca₂Mg₅Si₈O₂₂(OH)₂ + CaMg(CO₃)₂ + CO₂ +H₂O
This is a low-grade metamorphic change, occurring at temperature between about 250^oC and 450^oC. (MOM)

talc, calcite and quartz to tremolite, CO₂ and H₂O
5Mg₃Si₄O₁₀(OH)₂ + 6CaCO₃ +4SiO₂ → 3Ca₂Mg₅Si₈O₂₂(OH)₂ + 6CO₂ +2H₂O
Metamorphism of siliceous carbonate rock causes the formation of hydrous phases such as talc and tremolite. (DHZ 5B.127, 213)

tremolite and calcite to diopside, dolomite, CO₂ and H₂O
Ca₂Mg₅Si₈O₂₂(OH)₂ + 3CaCO₃ ⇌ 4CaMgSi₂O₆ + CaMg(CO₃)₂ + CO₂ + H₂O
The forward reaction is a diopside-forming metamorphic reaction. (DHZ 2A.249)

tremolite, calcite and quartz to diopside, CO₂ and H₂O
Ca₂Mg₅Si₈O₂₂(OH)₂ + 3CaCO₃ + 2SiO₂ → 5CaMgSi₂O₆ + 3CO₂ + H₂O
This is a medium-grade metamorphic change occurring at temperature between about 450^oC and 600^oC. (DHZ 2A p270, MOM)

tremolite and dolomite to forsterite, calcite, CO₂ and H₂O
Ca₂Mg₅Si₈O₂₂(OH)₂ + 11CaMg(CO₃)₂ → 8Mg₂SiO₄ + 13CaCO₃ + 9CO₂ + H₂O (DHZ 1A.264)

tremolite, dolomite and H₂O ⇆ hydroxylclinohumite, calcite and CO₂
Ca₂Mg₅Si₈O₂₂(OH)₂ + 13CaMg(CO₃)₂ + H₂O ⇆ 2Mg₉(SiO₄)₄(OH)₂ + 15CaCO₃ + 11CO₂
(DHZ 1A).

wollastonite and calcite to tilleyite and CO₂
2CaSiO₃ + 3CaCO₃ ⇌ Ca₅Si₂O₇(CO₃)₂+ CO₂
Higher temperatures favour the forward reaction (MM 34.1.1-16).

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