Dolomite (mineral)

Source: Wikipedia, the free encyclopedia.
Dolomite
Specific gravity
2.84–2.86
Optical propertiesUniaxial (−)
Refractive indexnω = 1.679–1.681
nε = 1.500
Birefringenceδ = 0.179–0.181
SolubilityPoorly soluble in dilute HCl
Other characteristicsMay fluoresce white to pink under UV; triboluminescent.
Ksp values vary between 10−19 and 10−17
References[2][3][4][5][6]
Photomicrograph
of a thin section in cross and plane polarised light: the brighter mineral grains in the picture are dolomite, and the darker grains are calcite.

Dolomite (

sedimentary carbonate rock composed mostly of the mineral dolomite (see Dolomite (rock)
). An alternative name sometimes used for the dolomitic rock type is dolostone.

History

Cristallo in the Dolomites mountain range near Cortina d'Ampezzo, Italy. The Dolomite Mountains were named after the mineral.

As stated by

Nicolas-Théodore de Saussure
first named the mineral (after Dolomieu) in March 1792.

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.[9] Crystal twinning
is common.

Solid solution exists between dolomite, the iron-dominant ankerite and the manganese-dominant kutnohorite.[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, and cobalt also can substitute in the structure for magnesium. The mineral dolomite is closely related to huntite Mg3Ca(CO3)4.

Because dolomite can be dissolved by slightly acidic water, areas where dolomite is an abundant rock-forming mineral are important as aquifers and contribute to karst terrain formation.[11]

Formation

Modern dolomite formation has been found to occur under

sulfate-reducing bacteria (e.g. Desulfovibrio brasiliensis),[15] but other microbial metabolisms have been also found to mediate in dolomite formation.[12] In general, low-temperature dolomite may occur in natural supersaturated environments rich in extracelullar polymeric substances (EPS) and microbial cell surfaces.[12] This is likely result from complexation of both magnesium and calcium by carboxylic acids comprising 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 irreversible

Ostwald'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 allocate dolomitization.[18] But the mineral is also volumetrically important in some Neogene platforms never subjected to elevated temperatures. Under such conditions of diagenesis the long-term activity of the deep biosphere could play a key role in dolomitization, since diagenetic fluids of contrasting composition are mixed as a response to Milankovitch cycles.[19]

A recent biotic synthetic experiment claims to have precipitated ordered dolomite when

Dalmatian dog, possibly as the result of an illness or infection.[21]

Uses

Dolomite is used as an ornamental stone, a concrete aggregate, and a source of

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 the pH of the water.

Calcined dolomite is also used as a

catalyst for destruction of tar in the gasification of biomass at high temperature.[22] 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.[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

References

  1. S2CID 235729616
    .
  2. ISBN 0-582-44210-9
    .
  3. ^ Dolomite Archived 2008-04-09 at the Wayback Machine. Handbook of Mineralogy. (PDF) . Retrieved on 2011-10-10.
  4. ^ "Dolomite". webmineral. Retrieved 12 March 2024.Archived 2005-08-27 at the Wayback Machine
  5. ^ "Dolomite". mindat.org. Retrieved 12 March 2024. Archived 2015-11-18 at the Wayback Machine. Mindat.org. Retrieved on 2011-10-10.
  6. ISBN 9780070358201. Archived
    from 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. ISBN 0-471-80580-7
  11. ^ Kaufmann, James. Sinkholes Archived 2013-06-04 at the Wayback Machine. USGS Fact Sheet. Retrieved on 2013-9-10.
  12. ^
    ISSN 0012-8252
    .
  13. PMID 32024862
    .
  14. ISSN 0012-8252
    .
  15. S2CID 4371495
    .
  16. PMID 23964124
    .
  17. ^ 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.
  18. ISSN 0012-8252
    .
  19. S2CID 234012426
    .
  20. S2CID 146426700
    .
  21. doi:10.1016/0016-7037(80)90264-1
    .
  22. ^ A Review of the Literature on Catalytic Biomass Tar Destruction Archived 2015-02-04 at the Wayback Machine National Renewable Energy Laboratory.
  23. ^ 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.
  24. ^ Calvo M.; Sevillano, E. (1991). "The Eugui quarries, Navarra, Spain". The Mineralogical Record. 22: 137–142.

External links

Wikimedia Commons has media related to Dolomite (mineral).
Retrieved from "https://en.wikipedia.org/w/index.php?title=Dolomite_(mineral)&oldid=1213331522"