Dolomite (rock)

Dolomite (also known as dolomite rock, dolostone 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 dolomite rock formed as a magnesium replacement of limestone or lime mud before lithification.[1] Dolomite rock 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. Dolomite rock can act as an oil and natural gas reservoir.

Triassic dolomitic rocks from Slovakia.
Erosion of dolomite over weaker shale created the Niagara Escarpment.
Trilobite fossil preserved as an internal mold in Silurian dolomite from southwestern Ohio, USA
Erosion of dolomitic rocks in Mourèze, Hérault, France.

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 dolomite rock from limestone was Belsazar Hacquet in 1778.[4]

Caves in dolomite rock

As with limestone caves, natural caves and solution tubes typically form in dolomite rock 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 dolomite rock. “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 caves around the world, they are usually in relatively small quantities and form in very fine-grained deposits.[5][8]

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. 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. Encyclopedia of Caves, (2005). Edited by Culver D.C and White W.B., ISBN 0-12-406061-7
  • Blatt, Harvey; Tracy, Robert J. (1996). Petrology; Igneous, Sedimentary, and Metamorphic (2nd ed.). W. H. Freeman. pp. 317–323. ISBN 0-7167-2438-3.
  • Tucker, M. E.; V. P., Wright (1990). Carbonate Sedimentology. Blackwell Scientific Publications. ISBN 0-632-01472-5.
  • Zenger, D. H.; Mazzullo, S. J. (1982). Dolomitization. Hutchinson Ross. ISBN 0-87933-416-9.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.