Wikipedia

Dolomite (mineral)

Dolomite(/ˈdɒl.əˌmaɪt,ˈdoʊ.lə-/) is ananhydrouscarbonate mineralcomposed ofcalciummagnesium carbonate,ideallyCaMg(CO3)2.The term is also used for asedimentarycarbonate rockcomposed mostly of the mineral dolomite (seeDolomite (rock)). An alternative name sometimes used for the dolomitic rock type is dolostone.

Dolomite
Dolomite (white) ontalc
General
CategoryCarbonate minerals
Formula
(repeating unit)		CaMg(CO3)2
IMA symbolDol[1]
Strunz classification5.AB.10
Crystal systemTrigonal
Crystal classRhombohedral (3)
H–M symbol:(3)
Space groupR3
Unit cella= 4.8012(1),
c= 16.002 [Å];Z= 3
Identification
ColorWhite, grey to pink, reddish-white, brownish-white; colourless in transmitted light
Crystal habitTabular crystals, often with curved faces, also columnar, stalactitic, granular, massive.
TwinningCommon as simple contact twins
Cleavage3 directions of cleavage not at right angles
FractureConchoidal
TenacityBrittle
Mohs scalehardness3.5–4.0
LusterVitreous to pearly
StreakWhite
Specific gravity2.84–2.86
Optical propertiesUniaxial (−)
Refractive indexnω= 1.679–1.681
nε= 1.500
Birefringenceδ= 0.179–0.181
SolubilityPoorly soluble in diluteHCl
Other characteristicsMayfluorescewhite to pink under UV;triboluminescent.
Kspvalues vary between 10−19and 10−17
References[2][3][4][5][6]
Dolomite andcalcitelook similar under amicroscope,butthin sectionscan be etched and stained in order to identify the minerals.Photomicrographof a thin section in cross and plane polarised light: the brighter mineral grains in the picture are dolomite, and the darker grains are calcite.

History

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Cristalloin theDolomitesmountain range nearCortina d'Ampezzo,Italy. The Dolomite Mountains were named after the mineral.

As stated byNicolas-Théodore de Saussure[7]the mineral dolomite was probably first described byCarl Linnaeusin 1768.[8]In 1791, it was described as a rock by the FrenchnaturalistandgeologistDéodat Gratet de Dolomieu(1750–1801), first in buildings of the old city of Rome, and later as samples collected in theTyrolean Alps.Nicolas-Théodore de Saussurefirst named the mineral (after Dolomieu) in March 1792.

Properties

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The mineral dolomite crystallizes in thetrigonal-rhombohedralsystem. 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 dilutehydrochloric acidascalcitedoes.[9]Crystal twinningis common.

Solid solutionexists between dolomite, theiron-dominantankeriteand themanganese-dominantkutnohorite.[10]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,andcobaltalso can substitute in the structure for magnesium. The mineral dolomite is closely related tohuntiteMg3Ca(CO3)4.

Because dolomite can be dissolved by slightly acidic water, areas where dolomite is an abundant rock-forming mineral are important asaquifersand contribute tokarstterrain formation.[11]

Formation

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Modern dolomite formation has been found to occur underanaerobicconditions insupersaturatedsalinelagoonssuch as those at theRio de Janeirocoast ofBrazil,namely, Lagoa Vermelha and Brejo do Espinho. There are many other localities where modern dolomite forms, notably alongsabkhasin thePersian Gulf,[12]but also in sedimentary basins bearing gas hydrates[13]and hypersaline lakes.[14]It is often thought that dolomite nucleates with the help ofsulfate-reducing bacteria(e.g.Desulfovibrio brasiliensis),[15]but othermicrobial metabolismshave been also found to mediate in dolomite formation.[12]In general, low-temperature dolomite may occur in natural supersaturated environments rich inextracelullar polymeric substances (EPS)and microbial cell surfaces.[12]This is likely result from complexation of both magnesium and calcium bycarboxylic acidscomprising EPS.[16]

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 are yet to be performed. Usually, the initial inorganic precipitation of a metastable "precursor" (such as magnesium calcite) can easily be achieved. The precursor phase will theoretically change gradually into a more stable phase (such as partially ordered dolomite) during periodical intervals of dissolution and re-precipitation. The general principle governing the course of this irreversiblegeochemicalreaction has been coined "breakingOstwald's step rule".[17]High diagenetic temperatures, such as those of groundwater flowing along deeply rooted fault systems affecting some sedimentary successions or deeply buried limestone rocks allocatedolomitization.[18]But the mineral is also volumetrically important in someNeogeneplatforms never subjected to elevated temperatures. Under such conditions ofdiagenesisthe long-term activity of thedeep biospherecould play a key role in dolomitization, since diagenetic fluids of contrasting composition are mixed as a response toMilankovitch cycles.[19]

A recent biotic synthetic experiment claims to have precipitated ordered dolomite whenanoxygenic photosynthesisproceeds in the presence of manganese(II).[20]A still perplexing example of an organogenic origin is that of the reported formation of dolomite in theurinary bladderof aDalmatiandog, possibly as the result of an illness or infection.[21]

Uses

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Dolomite is used as an ornamental stone, a concrete aggregate, and a source ofmagnesium oxide,as well as in thePidgeon processfor the production ofmagnesium.It is an importantpetroleumreservoirrock, and serves as the host rock for large strata-boundMississippi Valley-Type(MVT)oredeposits ofbase metalssuch aslead,zinc,andcopper.Wherecalcitelimestoneis uncommon or too costly, dolomite is sometimes used in its place as afluxfor thesmeltingof iron and steel. Large quantities of processed dolomite are used in the production offloat glass.

Inhorticulture,dolomite and dolomitic limestone are added to soils and soilless potting mixes as a pH buffer and as a magnesium source. Pastures can be limed with dolomitic lime to raise their pH and where there is a magnesium deficiency.

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

Calcined dolomite is also used as acatalystfor destruction oftarin thegasificationofbiomassat high temperature.[22]Particle physics researchers like to buildparticle detectorsunder 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 fromcosmic rayswithout adding tobackground radiationlevels.[23]

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.[24]

See also

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References

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  1. ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3): 291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
  2. ^Deer, W. A., R. A. Howie and J. Zussman (1966)An Introduction to the Rock Forming Minerals,Longman, pp. 489–493.ISBN0-582-44210-9.
  3. ^DolomiteArchived2008-04-09 at theWayback Machine.Handbook of Mineralogy. (PDF). Retrieved on 2011-10-10.
  4. ^"Dolomite".webmineral. Archived fromthe originalon 2005-08-27.Retrieved12 March2024.
  5. ^"Dolomite".mindat.org. Archived fromthe originalon 2015-11-18.Retrieved12 March2024..Mindat.org. Retrieved on 2011-10-10.
  6. ^Krauskopf, Konrad Bates; Bird, Dennis K. (1995).Introduction to geochemistry(3rd ed.). New York: McGraw-Hill.ISBN9780070358201.Archivedfrom the original on 2017-02-26.
  7. ^Saussure le fils, M. de (1792): Analyse de la dolomie. Journal de Physique, vol.40, pp.161-173.
  8. ^ Linnaeus, C. (1768): Systema naturae per regnum tria naturae, secundum classes, ordines, genera, species cum characteribus & differentiis. Tomus III. Laurentii Salvii, Holmiae, 236 p. On p.41 of this very book, Linnaeus stated (in Latin): "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 "".
  9. ^"Dolomite Mineral - Uses and Properties".geology.com.
  10. ^Klein, Cornelis and Cornelius S. Hurlbut Jr.,Manual of Mineralogy,Wiley, 20th ed., p. 339-340ISBN0-471-80580-7
  11. ^Kaufmann, James.SinkholesArchived2013-06-04 at theWayback Machine.USGS Fact Sheet. Retrieved on 2013-9-10.
  12. ^abcPetrash, Daniel A.; Bialik, Or M.; Bontognali, Tomaso R.R.; Vasconcelos, Crisógono; Roberts, Jennifer A.; McKenzie, Judith A.; Konhauser, Kurt O. (2017-08-01)."Microbially catalyzed dolomite formation: From near-surface to burial".Earth-Science Reviews.171:558–582.Bibcode:2017ESRv..171..558P.doi:10.1016/j.earscirev.2017.06.015.ISSN0012-8252.
  13. ^Snyder, Glen T.; Matsumoto, Ryo; Suzuki, Yohey; Kouduka, Mariko; Kakizaki, Yoshihiro; Zhang, Naizhong; Tomaru, Hitoshi; Sano, Yuji; Takahata, Naoto; Tanaka, Kentaro; Bowden, Stephen A. (2020-02-05)."Evidence in the Japan Sea of microdolomite mineralization within gas hydrate microbiomes".Scientific Reports.10(1): 1876.Bibcode:2020NatSR..10.1876S.doi:10.1038/s41598-020-58723-y.ISSN2045-2322.PMC7002378.PMID32024862.
  14. ^Last, William M. (1990-05-01)."Lacustrine dolomite—an overview of modern, Holocene, and Pleistocene occurrences".Earth-Science Reviews.27(3): 221–263.Bibcode:1990ESRv...27..221L.doi:10.1016/0012-8252(90)90004-F.ISSN0012-8252.
  15. ^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.S2CID4371495.
  16. ^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.PMC3767548.PMID23964124.
  17. ^Deelman, J.C. (1999):"Low-temperature nucleation of magnesite and dolomite"Archived2008-04-09 at theWayback Machine,Neues Jahrbuch für Mineralogie,Monatshefte, pp. 289–302.
  18. ^Warren, J. (2000-11-01)."Dolomite: occurrence, evolution and economically important associations".Earth-Science Reviews.52(1–3): 1–81.Bibcode:2000ESRv...52....1W.doi:10.1016/S0012-8252(00)00022-2.ISSN0012-8252.
  19. ^Petrash, Daniel A.; Bialik, Or M.; Staudigel, Philip T.; Konhauser, Kurt O.; Budd, David A. (2021)."Biogeochemical reappraisal of the freshwater–seawater mixing-zone diagenetic model".Sedimentology.68(5): 1797–1830.doi:10.1111/sed.12849.ISSN1365-3091.S2CID234012426.
  20. ^Daye, Mirna; Higgins, John; Bosak, Tanja (2019-06-01)."Formation of ordered dolomite in anaerobic photosynthetic biofilms".Geology.47(6): 509–512.Bibcode:2019Geo....47..509D.doi:10.1130/G45821.1.hdl:1721.1/126802.ISSN0091-7613.S2CID146426700.
  21. ^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.
  22. ^A Review of the Literature on Catalytic Biomass Tar DestructionArchived2015-02-04 at theWayback MachineNational Renewable Energy Laboratory.
  23. ^Short Sharp Science: Particle quest: Hunting for Italian WIMPs undergroundArchived2017-05-17 at theWayback Machine.Newscientist.com (2011-09-05). Retrieved on 2011-10-10.
  24. ^Calvo M.; Sevillano, E. (1991). "The Eugui quarries, Navarra, Spain".The Mineralogical Record.22:137–142.
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