Dolomite ( /ˈdɒləmaɪt/) 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.
Dolomite (white) on talc
|Crystal class||Rhombohedral (3) |
H-M symbol: (3)
|Unit cell||a = 4.8012(1), c = 16.002 [Å]; Z = 3|
|Color||White, 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|
|Mohs scale hardness||3.5 to 4|
|Luster||Vitreous to pearly|
|Optical properties||Uniaxial (-)|
|Refractive index||nω = 1.679–1.681 nε = 1.500|
|Birefringence||δ = 0.179–0.181|
|Solubility||Poorly soluble in dilute HCl|
|Other characteristics||May fluoresce white to pink under UV; triboluminescent. |
Ksp values vary between 1x10−19 to 1x10−17
Most probably the mineral dolomite was first described by Carl Linnaeus in 1768. 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.
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. Crystal twinning is common.
Solid solution exists between dolomite, the iron-dominant ankerite and the manganese-dominant kutnohorite. 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.
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). 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.
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".
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.
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.
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.
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
The Antrim Shale is a formation of Upper Devonian age in the Michigan Basin, in the US state of Michigan, and extending into Ohio and Indiana. It is a major source of natural gas in the northern part of the basin.
The Antrim Shale was defined by A. C. Lane in 1901, and named for type-section exposures in Antrim County, Michigan. The formation was previously known as the St. Cleric Shale in Michigan, and the Genessee Shale in Indiana.Berea Sandstone
Berea Sandstone, also known as Berea Grit, is a sandstone formation in the U.S. states of Michigan, Ohio, Pennsylvania, West Virginia, and Kentucky. It is named after Berea, Ohio. The sandstone has been used as a building stone and is a source of oil and gas.Brassfield Formation
The Brassfield Formation, named by A.F. Foerste in 1906, is a limestone and dolomite formation exposed in Arkansas, Ohio, Kentucky, Indiana, Tennessee and West Virginia in the United States. It is Early Silurian (Aeronian, Llandoverian) in age and well known for its abundant echinoderms, corals and stromatoporoids. In Ohio, where the unit has escaped dolomitization, the Brassfield is an encrinite biosparite with numerous crinoid species.Detroit River Group
The Detroit River Group is a geologic group in Michigan. It preserves fossils dating back to the Devonian period.Dolomite, California
Dolomite is an unincorporated community in Inyo County, California. It is located on the Southern Pacific Railroad 6.5 miles (10.5 km) south of New York Butte in the Owens Valley, at an elevation of 3674 feet (1120 m).Originally, in 1883, a siding on the Carson and Colorado Railroad, the town developed in 1885, when the Inyo Marble Company opened a quarry at the site.A number of Western films have been shot in Dolomite, including Sinister Journey (1948), From Hell to Texas (1958), Hell Bent for Leather (1960), An Eye For An Eye (1966), Nevada Smith (1966) and Waterhole No. 3 (1967).Dolomites
The Dolomites (Italian: Dolomiti [doloˈmiːti]; Ladin: Dolomites; German: Dolomiten [doːloːˈmɪtn̩] (listen); Venetian: Dołomiti [doɰoˈmiti]: Friulian: Dolomitis) are a mountain range located in northeastern Italy. They form a part of the Southern Limestone Alps and extend from the River Adige in the west to the Piave Valley (Pieve di Cadore) in the east. The northern and southern borders are defined by the Puster Valley and the Sugana Valley (Italian: Valsugana). The Dolomites are nearly equally shared between the provinces of Belluno, South Tyrol and Trentino.
Other mountain groups of similar geological structure spread along the River Piave to the east – Dolomiti d'Oltrepiave; and far away over the Adige River to the west – Dolomiti di Brenta (Western Dolomites). A smaller group is called Piccole Dolomiti (Little Dolomites), located between the provinces of Trentino, Verona, and Vicenza (see map).
The Dolomiti Bellunesi National Park and many other regional parks are located in the Dolomites. In August 2009, the Dolomites were declared a UNESCO World Heritage Site.Dolostone
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.
The term dolostone was introduced to avoid confusion with the mineral dolomite. The usage of the term dolostone is controversial because the name dolomite was first applied to the rock during the late 18th century and thus has technical precedence. The use of the term dolostone is not recommended by the Glossary of Geology published by the American Geological Institute. It is, however, used in some geological publications.
The geological process of conversion of calcite to dolomite is known as dolomitization and any intermediate product is known as "dolomitic limestone."The "dolomite problem" refers to the vast worldwide depositions of dolostone in past geologic record eluding a unified explanation for their formation.
The first geologist to distinguish dolomite rock from limestone was Belsazar Hacquet in 1778.Eau Claire Formation
The Eau Claire Formation is a geologic formation in the north central United States. It preserves trilobite fossils from the Cambrian Period.Karst
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 (perhaps by debris) 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.
The study of karst is considered of prime importance in petroleum geology since as much as 50% of the world's hydrocarbon reserves are hosted in porous karst systems.Lockport Dolomite
The Lockport Dolomite is a geologic formation in Ohio. It preserves fossils dating back to the Silurian period.Manitoulin Dolomite
The Manitoulin Dolomite is a geologic formation in Ontario. It preserves fossils dating back to the Silurian period.Mount Simon Sandstone
The Mount Simon Sandstone is the basal sandstone of the Potsdam Sandstone. It was deposited in a nearshore environment, unconformably overlying Precambrian basement.It is overlain by the Eau Claire Formation or Ordovician strata. It is presumed to be Upper Cambrian in age, though not verified. See infobox for more details.The Mount Simon formation is the equivalent of the La Motte Sandstone formation in the St. Francois Mountains of Missouri.Rochester Shale
The Rochester Shale is a geologic formation in West Virginia. It preserves fossils dating back to the Silurian period.St. Peter Sandstone
The St. Peter Sandstone is an Ordovician formation in the Chazyan stage of the Champlainian series. This sandstone originated as a sheet of sand in clear, shallow water near the shore of a Paleozoic sea and consists of fine-to-medium-size, well-rounded quartz grains with frosted surfaces. The extent of the formation spans north-south from Minnesota to Arkansas and east-west from Illinois into Nebraska and South Dakota. The formation was named by Owen (1847) after the Minnesota River, then known as the St. Peter River. The type locality is at the confluence of the Mississippi and Minnesota Rivers near Fort Snelling, Minnesota. In eastern Missouri the stone consists of quartz sand that is 99.44% silica.Sunbury Shale
The Sunbury Shale is a geologic formation in Michigan. It preserves fossils dating back to the Mississippian period.Swift Run Formation
The Swift Run Formation is a geologic formation in Virginia and West Virginia. It dates back to the Neoproterozoic.Trenton Formation
The Trenton Formation is a geologic formation in Michigan. It preserves fossils dating back to the Ordovician period.Triumph Dolomite
The Triumph Dolomite popular small saloon car was produced by the Triumph Motor Company division of the British Leyland Corporation in Canley, Coventry between October 1972 and August 1980.Warsaw Formation
The Warsaw Formation is a geologic formation in Illinois, Iowa and Missouri. It preserves fossils dating back to the Mississippian subperiod.