Dolostone

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Triassic dolomitic rocks from Slovakia. 7092 pieskovna Dolinka pri Hradisti pod Vratnom dolomit.JPG
Triassic dolomitic rocks from Slovakia.
Erosion of dolomite over weaker shale created the Niagara Escarpment. Canadian Horseshoe Falls with city of Niagara Falls, Ontario in background.jpg
Erosion of dolomite over weaker shale created the Niagara Escarpment.
Trilobite fossil preserved as an internal mold in Silurian dolostone from southwestern Ohio, USA Sthenarocalymene celebra - Arthropoda, Trilobita, Polymerida, Calymenidae - Silurian - Ohio, USA.jpg
Trilobite fossil preserved as an internal mold in Silurian dolostone from southwestern Ohio, USA
Erosion of dolomitic rocks in Moureze, Herault, France. Cirque de Moureze, Herault 32.jpg
Erosion of dolomitic rocks in Mourèze, Hérault, France.

Dolostone (also known as dolomite, dolomite rock or dolomitic 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 dolomites or magnesium-rich limestones. Dolomite has a stoichiometric ratio of nearly equal amounts of magnesium and calcium. Most dolostone formed as a magnesium replacement of limestone or lime mud before lithification. [1] Dolostone 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 (karst) over time. Dolostone can act as an oil and natural gas reservoir.

Contents

The term dolostone was introduced in 1948 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 was not recommended by the Glossary of Geology published by the American Geological Institute. [2]

The geological process of conversion of calcite to dolomite is known as dolomitization and any intermediate product is known as "dolomitic limestone." [3]

The "dolomite problem" refers to the vast worldwide depositions of dolomite in the past geologic record eluding a unified explanation for their formation.

The first geologist to distinguish dolostone from limestone was Belsazar Hacquet in 1778. [4]

Caves in dolostone

As with limestone caves, natural caves and solution tubes typically form in dolostone as a result of the dissolution by weak carbonic acid. [5] [6] Caves can also, less commonly, form through dissolution of rock by sulfuric acid. [7] Calcium carbonate speleothems (secondary deposits) in the forms of stalactites, stalagmites, flowstone etc., can also form in caves within dolostone. “Dolomite is a common rock type, but a relatively uncommon mineral in speleothems”. [5] Both the 'Union Internationale de Spéléologie' (UIS) and the American 'National Speleological Society' (NSS), extensively use in their publications, the terms "dolomite" or "dolomite rock" when referring to the natural bedrock containing a high percentage of CaMg(CO3)2 in which natural caves or solution tubes have formed. [5] [8]

Dolomite speleothems

Both calcium and magnesium go into solution when dolomite rock is dissolved. The speleothem precipitation sequence is: calcite, Mg-calcite, aragonite, huntite and hydromagnesite. [5] [8] Hence, the most common speleothem (secondary deposit) in caves within dolomite rock karst, is calcium carbonate in the most stable polymorph form of calcite. Speleothem types known to have a dolomite constituent include: coatings, crusts, moonmilk, flowstone, coralloids, powder, spar and rafts. [5] Although there are reports of dolomite speleothems known to exist in a number of cave around the world, they are usually in relatively small quantities and form in very fine-grained deposits. [5] [8]

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 dolomite, which contains a high percentage of the mineral dolomite, CaMg(CO3)2. In old USGS publications, dolomite was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolomites or magnesium-rich limestones.

Stalactite elongated mineral formation which hangs down from a cave ceiling

A stalactite is a type of formation that hangs from the ceiling of caves, hot springs, or manmade structures such as bridges and mines. Any material that is soluble, can be deposited as a colloid, or is in suspension, or is capable of being melted, may form a stalactite. Stalactites may be composed of lava, minerals, mud, peat, pitch, sand, sinter, and amberat. A stalactite is not necessarily a speleothem, though speleothems are the most common form of stalactite because of the abundance of limestone caves.

Calcite Carbonate mineral and polymorph of calcium carbonate

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".

Dolomite (mineral) carbonate mineral - CaMg(CO₃)₂

Dolomite 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.

Stalagmite Elongate mineral formation found on a cave floor

A stalagmite is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites may be composed of lava, minerals, mud, peat, pitch, sand, sinter and amberat.

Speleothem A structure formed in a cave by the deposition of minerals from water

Speleothems, commonly known as cave formations, are secondary mineral deposits formed in a cave. Speleothems typically form in limestone or dolomite solutional caves. The term "speleothem," as first introduced by Moore (1952), is derived from the Greek words spēlaion "cave" + théma "deposit". The definition of "speleothem," in most publications, specifically excludes secondary mineral deposits in mines, tunnels, and other man-made structures. Hill and Forti more concisely defined "secondary minerals" which create speleothems in caves:

A "secondary" mineral is one which is derived by a physicochemical reaction from a primary mineral in bedrock or detritus, and/or deposited because of a unique set of conditions in a cave; i.e., the cave environment has influenced the mineral's deposition.

Soda straw

A soda straw is a speleothem in the form of a hollow mineral cylindrical tube. They are also known as tubular stalactites. Soda straws grow in places where water leaches slowly through cracks in rock, such as on the roofs of caves. Soda straws in caves rarely grow more than a few millimetres per year and may average one tenth of a millimetre per year. A soda straw can turn into a stalactite if the hole at the bottom is blocked, or if the water begins flowing on the outside surface of the hollow tube.

Flowstone

Flowstones are composed of sheetlike deposits of calcite or other carbonate minerals, formed where water flows down the walls or along the floors of a cave. They are typically found in "solution caves", in limestone, where they are the most common speleothem. However, they may form in any type of cave where water enters that has picked up dissolved minerals. Flowstones are formed via the degassing of vadose percolation waters.

Cave popcorn common cave formation

Cave popcorn, or coralloids, are small nodes of calcite, aragonite or gypsum that form on surfaces in caves, especially limestone caves. They are a common type of speleothem.

Carbonate rock class of sedimentary 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 dolomite rock, also known as dolostone, which is composed of mineral dolomite (CaMg(CO3)2).

Cave of the Mounds cave in United States of America

Cave of the Mounds, a natural limestone cave located near Blue Mounds, Wisconsin, United States, is named for two nearby hills called the Blue Mounds. It is located in the southern slope of the east hill. The cave's beauty comes from its many varieties of mineral formations called speleothems. The Chicago Academy of Sciences considers the Cave of the Mounds to be "the significant cave of the upper Midwest" because of its beauty, and it is promoted as the "jewel box" of major American caves. In 1987, the United States Department of the Interior and the National Park Service designated the cave as a National Natural Landmark.

Rimstone

Rimstone, also called gours, is a type of speleothem in the form of a stone dam. Rimstone is made up of calcite and other minerals that build up in cave pools. The formation created, which looks like stairs, often extends into flowstone above or below the original rimstone. Often, rimstone is covered with small, micro-gours on horizontal surfaces. Rimstone basins may form terraces that extend over hundreds of feet, with single basins known up to 200 feet long from Tham Xe Biang Fai in Laos

Solutional cave cave formed in soluble rock such as limestone, chalk, dolomite, marble, salt beds or gypsum

A solutional cave or karst cave is a cave usually formed in the soluble rock limestone. It is the most frequently occurring type of cave. It can also form in other rocks, including chalk, dolomite, marble, salt beds, and gypsum.

Concrete degradation Concrete technology

Concrete degradation may have various causes. Concrete can be damaged by fire, aggregate expansion, sea water effects, bacterial corrosion, calcium leaching, physical damage and chemical damage. This process adversely affects concrete exposed to these damaging stimuli.

Caymanite

Caymanite at its type area is an uncommon variety of dolomite, also known as dolostone, originally reported from locations in the Miocene Cayman Formation in the Cayman Islands: the Bluff in Cayman Brac and the East End on Grand Cayman.

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.

Dolomitization is a geological process by which the carbonate mineral dolomite is formed when magnesium ions replace calcium ions in another carbonate mineral, calcite. It is common for this mineral alteration into dolomite to take place due to evaporation of water in the sabkha area. Dolomitization involves substantial amount of recrystallization. This process is described by the stoichiometric equation:

Calcite rafts

Calcite crystals form on the surface of quiescent bodies of water, even when the bulk water is not supersaturated with respect to calcium carbonate. The crystals grow, attach to one other and appear to be floating rafts of a white, opaque material. The floating materials have been referred to as calcite rafts or "leopard spots".

Indiana Caverns

Indiana Caverns is part of the Binkley Cave system near Corydon, Indiana.

Calthemite Secondary calcium carbonate deposit growing under man-made structures

Calthemite is a secondary deposit, derived from concrete, lime, mortar or other calcareous material outside the cave environment. Calthemites grow on or under, man-made structures and mimic the shapes and forms of cave speleothems, such as stalactites, stalagmites, flowstone etc. Calthemite is derived from the Latin calx "lime" + Latin < Greek théma, "deposit" meaning ‘something laid down’, and the Latin –ita < Greek -itēs – used as a suffix indicating a mineral or rock. The term "speleothem", due to its definition can only be used to describe secondary deposits in caves and does not include secondary deposits outside the cave environment.

References

  1. Zenger & Mazzullo, 1982
  2. Neuendorf, K.K.E.; Mehl, Jr., J.P.; Jackson, J.A. (editors) (2005). Glossary of Geology (5th edition). Alexandria, Virginia: American Geological Institute. p. 189. ISBN   978-0922152896.CS1 maint: extra text: authors list (link)
  3. "Dolomite. A sedimentary rock known as dolostone or dolomite rock". Geology.com. Retrieved 20 June 2014.
  4. Kranjc, Andrej (2006). "Balthasar Hacquet (1739/40-1815), the Pioneer of Karst Geomorphologists". Acta Carsologica. Institute for the Karst Research, Scientific Research Centre, Slovenian Academy of Sciences and Arts. 35 (2). ISSN   0583-6050. Archived from the original on 31 December 2016.
  5. 1 2 3 4 5 6 Hill, C A and Forti, P, (1997). Cave Minerals of the World, Second editions. [Huntsville, Alabama: National Speleological Society Inc.] pp 14, 142, 143, 144 & 150, ISBN   1-879961-07-5
  6. White W.B and Culver D.C., (2005) Chapter "Caves, Definitions of", Encyclopedia of Caves, edited by Culver D.C and White W.B., ISBN   0-12-406061-7
  7. Polyak, Victor J.; Provencio, Paula (2000). "By-product materials relatied to H2S-H2SO4-influenced speleogenesis of Carlsbad, Lechuguilla, and other caves of the Guadalupe Mountains, New Mexico". Journal of Cave and Karst Studies. 63 (1): 23–32. Retrieved 4 April 2020.
  8. 1 2 3 Encyclopedia of Caves, (2005). Edited by Culver D.C and White W.B., ISBN   0-12-406061-7