Whewellite

Mineral
(repeating unit)CaC2O4·H2OIMA symbolWhe[1]Strunz classification10.AB.45Crystal systemMonoclinicCrystal classPrismatic (2/m)
(same H-M symbol)Space groupP21/c (no. 14)IdentificationColorColorless, yellowish, brownishCrystal habitEquant or stout prismatic crystalsTwinninge {101} twin planeCleavage{101} good, {010} imperfect, {001} indistinct, {110} indistinctFractureConchoidalTenacityBrittleMohs scale hardness2.5–3LusterVitreous to pearlyDiaphaneityTransparentSpecific gravity2.23Optical propertiesBiaxial (+), colorless (transmitted light)SolubilityInsoluble in water, soluble in acidsReferences[2][3][4][5]

Whewellite /ˈhjuːəlaɪt/ is a mineral, hydrated calcium oxalate, formula Ca C2O4·H2O. Because of its organic content it is thought to have an indirect biological origin; this hypothesis is supported by its presence in coal and sedimentary nodules. However, it has also been found in hydrothermal deposits where a biological source appears improbable. For this reason, it may be classed as a true mineral.

Whewellite, or at least crystalline calcium oxalate, does also arise from biological sources. Small crystals or flakes of it are sometimes found on the surfaces of some cacti, and kidney stones frequently have the same composition.

Whewellite was named after William Whewell (1794–1866), an English polymath, naturalist and scientist, professor of moral philosophy at Cambridge and inventor of the system of crystallographic indexing.[2]

Heat decomposition

Whewellite (calcium oxalate monohydrate) heat decomposition mass curve. The whewellite decomposes first to anhydrous calcium oxalate, then to calcium carbonate (losing carbon monoxide), and finally to calcium oxide (losing carbon dioxide).

Whewellite is used as a thermogravimetric analysis standard due to its well-known decomposition temperatures and products.

See also

References

  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. S2CID 235729616.
  2. ^ a b Whewellite: mindat.org
  3. ^ Webmineral.com
  4. ^ Handbook of Mineralogy
  5. ^ Tazzoli, V.; Domeneghetti, M.C. (1980). "The crystal structures of whewellite and weddellite: re-examination and comparison". American Mineralogist. 65: 327–334. Retrieved 31 December 2020.
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Bibliography

  • Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 1099–1101.
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