Vaterite

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Vaterite
Vaterite2-San Vito, Monte Somma, Italy.tif
Vaterite from San Vito quarry, San Vito, Monte Somma, Somma-Vesuvius Complex, Italy
General
CategoryCarbonate minerals
Formula
(repeating unit)
CaCO3
Strunz classification5.AB.20
Crystal systemHexagonal
Crystal classDihexagonal dipyramidal (6mmm)
H-M symbol: (6/m 2/m 2/m)
Space groupP63/mmc {P63/m 2/m 2/c}
Unit cella = 4.13, c = 8.49 [Å]; Z = 6
Identification
ColorColorless
Crystal habitFine fibrous crystals, typically less than 0.1 mm, in spherulitic aggregates.
FractureIrregular to uneven, splintery
TenacityBrittle
Mohs scale hardness3
LusterSub-vitreous, waxy
DiaphaneityTransparent to semi-transparent
Specific gravity2.54
Optical propertiesUniaxial (+)
Refractive indexnω = 1.550 nε = 1.650
Birefringenceδ = 0.100
References[1][2][3]

Vaterite is a mineral, a polymorph of calcium carbonate (CaCO3). It was named after the German mineralogist Heinrich Vater. It is also known as mu-calcium carbonate (μ-CaCO3) and has a JCPDS number of 13-192. Vaterite belongs to the hexagonal crystal system, whereas calcite is trigonal and aragonite is orthorhombic.

Vaterite, like aragonite, is a metastable phase of calcium carbonate at ambient conditions at the surface of the earth. As it is less stable than either calcite or aragonite, vaterite has a higher solubility than either of these phases. Therefore, once vaterite is exposed to water, it converts to calcite (at low temperature) or aragonite (at high temperature: ~60 °C). At 37 °C for example a solution-mediated transition from vaterite to calcite occurs, where the latter one dissolves and subsequently precipitates as calcite assisted by an Ostwald ripening process.[4]

However, vaterite does occur naturally in mineral springs, organic tissue, gallstones, urinary calculi and plants. In those circumstances, some impurities (metal ions or organic matter) may stabilize the vaterite and prevent its transformation into calcite or aragonite. Vaterite is usually colorless, its shape is spherical, and its diameter is small, ranging from 0.05 to 5 μm.

Vaterite can be produced as the first mineral deposits repairing natural or experimentally-induced shell damage in some aragonite-shelled mollusks (e.g. gastropods). Subsequent shell deposition occurs as aragonite. In 2018, vaterite was identified as a constituent of a deposit formed on the leaves of Saxifraga at Cambridge University Botanic Garden.[5][6]

Vaterites of the locality San Vito (Monte Somma, Italy) are microcrystalline with largest crystals below 2 mm size. This vaterite is epitactic after aragonite. The crystal contains triplet of aragonite inside of it. On the its termination twin seams of aragonite triplet are well visible.


See also[edit]

References[edit]

  1. ^ Mindat.org
  2. ^ Handbook of Mineralogy
  3. ^ Webmineral data
  4. ^ Zhou,, Gen-Tao; Yao,, Qi-Zhi; Fu,, Sheng-Quan; Guan, Ye-Bin (2010). "Controlled crystallization of unstable vaterite with distinct morphologies and their polymorphic transition to stable calcite". Eur. J. Mineralogy. doi:10.1127/0935-1221/2009/0022-2008.
  5. ^ Chris Elliott (12 Mar 2018). "Incredible discovery at Cambridge's Botanic Garden that could transform treatment of cancer". Cambridge News. Archived from the original on 2018-03-12.
  6. ^ "Rare mineral discovered in plants for first time". Science Daily. 5 Mar 2018.