Calcite

Calcite
Clockwise from top left: scalenohedral, rhomboedral, stalactitic, and botryoidal calcite
General
CategoryCarbonate mineral
Formula
(repeating unit)
CaCO3
Strunz classification5.AB.05
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupR3c
Unit cella = 4.9896(2) Å,
c = 17.0610(11) Å; Z = 6
Identification
ColorTypically colorless or creamy white - may have shades of brownish colors
Crystal habitBotryoidal, concretionary, druse, globular, granular, massive, rhombohedral, scalenohedral, stalactitic
TwinningCommon by four twin laws
CleavagePerfect on {1011} three directions with angle of 74° 55'[1]
FractureConchoidal
TenacityBrittle
Mohs scale hardness3 (defining mineral)
LusterVitreous to pearly on cleavage surfaces
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.71
Optical propertiesUniaxial (−); low relief
Refractive indexnω = 1.640–1.660
nε = 1.486
Birefringenceδ = 0.154–0.174
FusibilityInfusible (decrepitates energetically)[2]
SolubilitySoluble in dilute acids
Other characteristicsMay fluoresce red, blue, yellow, and other colors under either SW and LW UV; phosphorescent
References[3][4][5]

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses.

Other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C,[6][7] and vaterite is even less stable.

  1. ^ Klein, Cornelis; Hurlbut, Cornelius S. Jr. (1993). Manual of mineralogy: (after James D. Dana) (21st ed.). New York: Wiley. p. 405. ISBN 047157452X.
  2. ^ Cite error: The named reference Sinkankas1964 was invoked but never defined (see the help page).
  3. ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2003). "Calcite" (PDF). Handbook of Mineralogy. Vol. V (Borates, Carbonates, Sulfates). Chantilly, VA, US: Mineralogical Society of America. ISBN 978-0962209741.
  4. ^ Cite error: The named reference mindat was invoked but never defined (see the help page).
  5. ^ Barthelmy, Dave. "Calcite Mineral Data". webmineral.com. Retrieved 6 May 2018.
  6. ^ Yoshioka S.; Kitano Y. (1985). "Transformation of aragonite to calcite through heating". Geochemical Journal. 19 (4): 24–249. Bibcode:1985GeocJ..19..245Y. doi:10.2343/geochemj.19.245.
  7. ^ Staudigel P. T.; Swart P. K. (2016). "Isotopic behavior during the aragonite-calcite transition: Implications for sample preparation and proxy interpretation". Chemical Geology. 442: 130–138. Bibcode:2016ChGeo.442..130S. doi:10.1016/j.chemgeo.2016.09.013.

Calcite

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