Dolomite

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Dolomite
Dolomite Luzenac.jpg
Dolomite (white) on talc
General
Category Carbonate minerals
Formula
(repeating unit)
CaMg(CO3)2
Strunz classification 5.AB.10
Crystal system Trigonal
Crystal class Rhombohedral (3)
H-M symbol: (3)
Space group R3
Unit cell a = 4.8012(1), c = 16.002 [Å]; Z = 3
Identification
ColorWhite, gray to pink
Crystal habit Tabular crystals, often with curved faces, also columnar, stalactitic, granular, massive.
Twinning Common as simple contact twins
Cleavage 3 directions of cleavage not at right angles
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness3.5 to 4
Luster Vitreous to pearly
Streak White
Specific gravity 2.84–2.86
Optical propertiesUniaxial (-)
Refractive index nω = 1.679–1.681 nε = 1.500
Birefringence δ = 0.179–0.181
Solubility Poorly soluble in dilute HCl
Other characteristicsMay fluoresce white to pink under UV; triboluminescent.
Ksp values vary between 1x10−19 to 1x10−17
References [1] [2] [3] [4] [5]

Dolomite ( /ˈdɒləmt/ ) is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally CaMg(CO3)2. The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomitic rock type is dolostone.

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 techniques are used. In practice, however, it is very difficult to achieve perfect dryness; anhydrous compounds gradually absorb water from the atmosphere so they must be stored carefully.

Calcium Chemical element with atomic number 20

Calcium is a chemical element with 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 properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

Magnesium Chemical element with atomic number 12

Magnesium is a chemical element with symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.

Contents

History

Most probably the mineral dolomite was first described by Carl Linnaeus in 1768. [6] In 1791, it was described as a rock by the French naturalist and geologist Déodat Gratet de Dolomieu (1750–1801), first in buildings of the old city of Rome, and later as samples collected in the mountains now known as the Dolomite Alps of northern Italy. Nicolas-Théodore de Saussure first named the mineral (after Dolomieu) in March 1792. [7]

Carl Linnaeus Swedish botanist, physician, and zoologist

Carl Linnaeus, also known after his ennoblement as Carl von Linné, was a Swedish botanist, physician, and zoologist who formalised binomial nomenclature, the modern system of naming organisms. He is known as the "father of modern taxonomy". Many of his writings were in Latin, and his name is rendered in Latin as Carolus Linnæus.

Natural history study of organisms including plants or animals in their environment

Natural history is a domain of inquiry involving organisms including animals, fungi and plants in their environment; leaning more towards observational than experimental methods of study. A person who studies natural history is called a naturalist or natural historian.

Geologist Scientist who studies geology

A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes the Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, although backgrounds in physics, chemistry, biology, and other sciences are also useful. Field work is an important component of geology, although many subdisciplines incorporate laboratory work.

Properties

The mineral dolomite crystallizes in the trigonal-rhombohedral system. It forms white, tan, gray, or pink crystals. Dolomite is a double carbonate, having an alternating structural arrangement of calcium and magnesium ions. Unless it is in fine powder form, it does not rapidly dissolve or effervesce (fizz) in cold dilute hydrochloric acid as calcite does. [8] Crystal twinning is common.

Hydrochloric acid strong mineral acid

Hydrochloric acid or muriatic acid is a colorless inorganic chemical system with the formula H
2
O:HCl
. Hydrochloric acid has a distinctive pungent smell. It is classified as strongly acidic and can attack the skin over a wide composition range, since the hydrogen chloride completely dissociates in aqueous solution.

Calcite carbonate mineral

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite".

Crystal twinning when two separate crystals share some of the same crystal lattice points in a symmetrical manner

Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. The surface along which the lattice points are shared in twinned crystals is called a composition surface or twin plane.

Solid solution exists between dolomite, the iron-dominant ankerite and the manganese-dominant kutnohorite. [9] Small amounts of iron in the structure give the crystals a yellow to brown tint. Manganese substitutes in the structure also up to about three percent MnO. A high manganese content gives the crystals a rosy pink color. Lead, zinc, and cobalt also substitute in the structure for magnesium. The mineral dolomite is closely related to huntite Mg3Ca(CO3)4.

Solid solution Chemical solution in solid form; whose solvents crystal structure is not altered by solute

A solid solution is a solid-state solution of one or more solutes in a solvent. Such a multi-component system is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the chemical components remain in a single homogeneous phase. This often happens when the two elements involved are close together on the periodic table; conversely, a chemical compound generally results when two metals involved are not near each other on the periodic table.

Iron Chemical element with atomic number 26

Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space.

Ankerite mineral, calcium iron carbonate

Ankerite is a calcium, iron, magnesium, manganese carbonate mineral of the group of rhombohedral carbonates with formula: Ca(Fe,Mg,Mn)(CO3)2. In composition it is closely related to dolomite, but differs from this in having magnesium replaced by varying amounts of iron(II) and manganese. It forms a series with dolomite and kutnohorite.

Because dolomite can be dissolved by slightly acidic water, areas of dolomite are important as aquifers and contribute to karst terrain formation. [10]

Aquifer Underground layer of water-bearing permeable rock

An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials. Groundwater can be extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude, which is a solid, impermeable area underlying or overlying an aquifer. If the impermeable area overlies the aquifer, pressure could cause it to become a confined aquifer.

Karst Topography formed from the dissolution of soluble rocks

Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant rocks, such as quartzite, given the right conditions. Subterranean drainage may limit surface water, with few to no rivers or lakes. However, in regions where the dissolved bedrock is covered or confined by one or more superimposed non-soluble rock strata, distinctive karst features may occur only at subsurface levels and be totally missing above ground.

Formation

Modern dolomite formation has been found to occur under anaerobic conditions in supersaturated saline lagoons along the Rio de Janeiro coast of Brazil, namely, Lagoa Vermelha and Brejo do Espinho. It is often thought that dolomite will develop only with the help of sulfate-reducing bacteria (e.g. Desulfovibrio brasiliensis). [11] However, low-temperature dolomite may occur in natural environments rich in organic matter and microbial cell surfaces. This occurs as a result of magnesium complexation by carboxyl groups associated with organic matter. [12]

Hypoxia refers to low oxygen conditions. Normally, 20.9% of the gas in the atmosphere is oxygen. The partial pressure of oxygen in the atmosphere is 20.9% of the total barometric pressure. In water however, oxygen levels are much lower, approximately 1%, and fluctuate locally depending on the presence of photosynthetic organisms and relative distance to the surface.

Supersaturation State of a solution that contains more solute than can be dissolved at equilibrium

Supersaturation is a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. It can also refer to a vapor of a compound that has a higher (partial) pressure than the vapor pressure of that compound.

Lagoon A shallow body of water separated from a larger body of water by barrier islands or reefs

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Dolomite (white) with magnesite (yellowish) from Spain Dolomite-Magnesite- Navarre.jpg
Dolomite (white) with magnesite (yellowish) from Spain
Upper Triassic dolostone of the Choc Nappe in Slovakia 7092 pieskovna Dolinka pri Hradisti pod Vratnom dolomit.JPG
Upper Triassic dolostone of the Choč Nappe in Slovakia

Vast deposits of dolomite are present in the geological record, but the mineral is relatively rare in modern environments. Reproducible, inorganic low-temperature syntheses of dolomite and magnesite were published for the first time in 1999. Those laboratory experiments showed how the initial precipitation of a metastable "precursor" (such as magnesium calcite) will change gradually into more and more of the stable phase (such as dolomite or magnesite) during periodical intervals of dissolution and re-precipitation. The general principle governing the course of this irreversible geochemical reaction has been coined "breaking Ostwald's step rule". [13]

There is some evidence for a biogenic occurrence of dolomite. One example is that of the formation of dolomite in the urinary bladder of a Dalmatian dog, possibly as the result of an illness or infection. [14]

Uses

Dolomite is used as an ornamental stone, a concrete aggregate, and a source of magnesium oxide, as well as in the Pidgeon process for the production of magnesium. It is an important petroleum reservoir rock, and serves as the host rock for large strata-bound Mississippi Valley-Type (MVT) ore deposits of base metals such as lead, zinc, and copper. Where calcite limestone is uncommon or too costly, dolomite is sometimes used in its place as a flux for the smelting of iron and steel. Large quantities of processed dolomite are used in the production of float glass.

In horticulture, dolomite and dolomitic limestone are added to soils and soilless potting mixes as a pH buffer and as a magnesium source.

Dolomite is also used as the substrate in marine (saltwater) aquariums to help buffer changes in pH of the water.

Calcined dolomite is also used as a catalyst for destruction of tar in the gasification of biomass at high temperature. [15]

Dolomite (light pink) with chalcopyrite from the Tri-state district, Cherokee County, Kansas (size: 11.4x7.2x4.6 cm) Chalcopyrite-Dolomite-44427.jpg
Dolomite (light pink) with chalcopyrite from the Tri-state district, Cherokee County, Kansas (size: 11.4×7.2×4.6 cm)

Particle physics researchers like to build particle detectors under layers of dolomite to enable the detectors to detect the highest possible number of exotic particles. Because dolomite contains relatively minor quantities of radioactive materials, it can insulate against interference from cosmic rays without adding to background radiation levels. [16]

In addition to being an industrial mineral, dolomite is highly valued by collectors and museums when it forms large, transparent crystals. The specimens that appear in the magnesite quarry exploited in Eugui, Esteribar, Navarra (Spain) are considered among the best in the world [17]

See also

Related Research Articles

Limestone Sedimentary rocks made of calcium carbonate

Limestone is a carbonate sedimentary rock that is often composed of the skeletal fragments of marine organisms such as coral, foraminifera, and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). A closely related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg(CO3)2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones.

Mineral Element or chemical compound that is normally crystalline and that has been formed as a result of geological processes

A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings often synthesize inorganic minerals that also occur in rocks.

Aragonite carbonate mineral

Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, CaCO3 (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including precipitation from marine and freshwater environments.

Rhodochrosite manganese carbonate mineral

Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its (rare) pure form, it is typically a rose-red color, but impure specimens can be shades of pink to pale brown. It streaks white, and its Mohs hardness varies between 3.5 and 4. Its specific gravity is between 3.5 and 3.7. It crystallizes in the trigonal system, and cleaves with rhombohedral carbonate cleavage in three directions. Crystal twinning often is present. It is transparent to translucent with refractive indices of =1.814 to 1.816, =1.596 to 1.598. It is often confused with the manganese silicate, rhodonite, but is distinctly softer.

Magnesium carbonate chemical compound

Magnesium carbonate, MgCO3 (archaic name magnesia alba), is an inorganic salt that is a white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.

Ooid sedimentary grains

Ooids are small, spheroidal, "coated" (layered) sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals. Ooids usually form on the sea floor, most commonly in shallow tropical seas. After being buried under additional sediment, these ooid grains can be cemented together to form a sedimentary rock called an oolite. Oolites usually consist of calcium carbonate; these belong to the limestone rock family. Pisoids are similar to ooids, but are larger than 2 mm in diameter, often considerably larger, as with the pisoids in the hot springs at Carlsbad in the Czech Republic.

Skarn Hard, coarse-grained, hydrothermally altered metamorphic rocks

Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals. These minerals form as a result of alteration which occurs when hydrothermal fluids interact with a protolith of either igneous or sedimentary origin. In many cases, skarns are associated with the intrusion of a granitic pluton found in and around faults or Shear zones that intrude into a carbonate layer such as a dolomite or limestone. Skarns can form by regional, or contact metamorphism and therefore form in relatively high temperature environments. The hydrothermal fluids associated with the metasomatic processes can originate from either magmatic, metamorphic, meteoric, marine, or even a mix of these. The resulting skarn may consist of a variety of different minerals which are highly dependent on the original composition of both the hydrothermal fluid and the original composition of the protolith.

Magnesite carbonate mineral

Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Iron, manganese, cobalt and nickel may occur as admixtures, but only in small amounts.

Dolostone Sedimentary carbonate rock that contains a high percentage of the mineral dolomite

Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite, CaMg(CO3)2. In old USGS publications, it was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. Technically, dolostone has a stoichiometric ratio of nearly equal amounts of magnesium and calcium. Most dolostones formed as a magnesium replacement of limestone or lime mud prior to lithification. It is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater, but it can still develop solution features over time. Dolostone can act as an oil and natural gas reservoir.

Artinite carbonate mineral

Artinite is a hydrated magnesium carbonate mineral with formula: Mg2(CO3)(OH)2·3H2O. It forms white silky monoclinic prismatic crystals that are often in radial arrays or encrustations. It has a Mohs hardness of 2.5 and a specific gravity of 2.

Carbonate rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3) and dolostone, which is composed of the mineral dolomite (CaMg(CO3)2).

Déodat Gratet de Dolomieu French geologist, volcanologist and mineralogist

Dieudonné Sylvain Guy Tancrède de Gratet de Dolomieu usually known as Déodat de Dolomieu was a French geologist; the mineral and the rock dolomite and the largest summital crater on the Piton de la Fournaise volcano were named after him.

Talc carbonates are a suite of rock and mineral compositions found in metamorphic ultramafic rocks.

Kutnohorite carbonate mineral

Kutnohorite is a rare calcium manganese carbonate mineral with magnesium and iron that is a member of the dolomite group. It forms a series with dolomite, and with ankerite. The end member formula is CaMn2+(CO3)2, but Mg2+ and Fe2+ commonly substitute for Mn2+, with the Mn content varying from 38% to 84%, so the formula Ca(Mn2+,Mg,Fe2+)(CO3)2 better represents the species. It was named by Professor Bukowsky in 1901 after the type locality of Kutná Hora, Bohemia, in the Czech Republic. It was originally spelt “kutnahorite” but “kutnohorite” is the current IMA-approved spelling.

Neomorphism refers to the wet metamorphic process in which diagenetic alterations systematically transform minerals into either polymorphs or crystalline structures that are structurally identical to the rock(s) from which they developed.

Metamorphic facies

A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in the geological history of the area. The boundaries between facies are wide because they are gradational and approximate. The area on the graph corresponding to rock formation at the lowest values of temperature and pressure is the range of formation of sedimentary rocks, as opposed to metamorphic rocks, in a process called diagenesis.

Aragonite sea Chemical conditions of the sea favouring aragonite deposition

An aragonite sea contains aragonite and high-magnesium calcite as the primary inorganic calcium carbonate precipitates. The chemical conditions of the seawater must be notably high in magnesium content relative to calcium for an aragonite sea to form. This is in contrast to a calcite sea in which seawater low in magnesium content relative to calcium favors the formation of low-magnesium calcite as the primary inorganic marine calcium carbonate precipitate.

Huntite carbonate mineral

Huntite is a carbonate mineral with the chemical formula Mg3Ca(CO3)4. Huntite crystallizes in the trigonal system and typically occurs as platy crystals and powdery masses. The most common industrial use of huntite is as a natural mixture with hydromagnesite as a flame retardant or fire retardant additive for polymers.

References

  1. Deer, W. A., R. A. Howie and J. Zussman (1966) An Introduction to the Rock Forming Minerals, Longman, pp. 489–493. ISBN   0-582-44210-9.
  2. Dolomite Archived 2008-04-09 at the Wayback Machine . Handbook of Mineralogy. (PDF) . Retrieved on 2011-10-10.
  3. Dolomite Archived 2005-08-27 at the Wayback Machine . Webmineral. Retrieved on 2011-10-10.
  4. Dolomite Archived 2015-11-18 at the Wayback Machine . Mindat.org. Retrieved on 2011-10-10.
  5. Krauskopf, Konrad Bates; Bird, Dennis K. (1995). Introduction to geochemistry (3rd ed.). Newyork: McGraw-Hill. ISBN   9780070358201. Archived from the original on 2017-02-26.
  6. On p.41 of part 3 of his book "Systema naturae per regna tria naturae etc." (1768), Linnaeus stated: "Marmor tardum - Marmor paticulis subimpalpabilibus album diaphanum. Hoc simile quartzo durum, distinctum quod cum aqua forti non, nisi post aliquot minuta & fero, effervescens." In translation: "Slow marble - Marble, white and transparent with barely discernable particles. This is as hard as quartz, but it is different in that it does not, unless after a few minutes, effervesce with "aqua forti"".
  7. Saussure le fils, M. de (1792): Analyse de la dolomie. Journal de Physique, vol.40, pp.161-173.
  8. "Dolomite Mineral - Uses and Properties". geology.com.
  9. Klein, Cornelis and Cornelius S. Hurlbut Jr., Manual of Mineralogy, Wiley, 20th ed., p. 339-340 ISBN   0-471-80580-7
  10. Kaufmann, James. Sinkholes Archived 2013-06-04 at the Wayback Machine . USGS Fact Sheet. Retrieved on 2013-9-10.
  11. Vasconcelos C.; McKenzie J. A.; Bernasconi S.; Grujic D.; Tien A. J. (1995). "Microbial mediation as a possible mechanism for natural dolomite formation at low temperatures". Nature. 337 (6546): 220–222. Bibcode:1995Natur.377..220V. doi:10.1038/377220a0.
  12. Roberts, J. A.; Kenward, P. A.; Fowle, D. A.; Goldstein, R. H.; Gonzalez, L. A. & Moore, D. S. (1980). "Surface chemistry allows for abiotic precipitation of dolomite at low temperature". Proceedings of the National Academy of Sciences of the United States of America. 110 (36): 14540–5. Bibcode:2013PNAS..11014540R. doi:10.1073/pnas.1305403110. PMC   3767548 . PMID   23964124.
  13. Deelman, J.C. (1999): "Low-temperature nucleation of magnesite and dolomite" Archived 2008-04-09 at the Wayback Machine , Neues Jahrbuch für Mineralogie, Monatshefte, pp. 289–302.
  14. Mansfield, Charles F. (1980). "A urolith of biogenic dolomite – another clue in the dolomite mystery". Geochimica et Cosmochimica Acta. 44 (6): 829–839. Bibcode:1980GeCoA..44..829M. doi:10.1016/0016-7037(80)90264-1.
  15. A Review of the Literature on Catalytic Biomass Tar Destruction Archived 2015-02-04 at the Wayback Machine National Renewable Energy Laboratory.
  16. Short Sharp Science: Particle quest: Hunting for Italian WIMPs underground Archived 2017-05-17 at the Wayback Machine . Newscientist.com (2011-09-05). Retrieved on 2011-10-10.
  17. Calvo M.; Sevillano, E. (1991). "The Eugui quarries, Navarra, Spain". The Mineralogical Record. 22: 137–142.