Calcium oxalate

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White, crystalline powder that occurs naturally as the minerals whewellite and weddellite. Calcium oxalate also occurs in some plants such as dumb cane, rhubarb and spinach. The powdered mineral is used in ceramic glazes. Calcium oxalate forms naturally on the surface of weathered calcareous stones due to reaction of oxalic acid excretions from some types of lichen and fungi. Since calcium oxalate is less soluble than calcium carbonate in acids, the production of thin films of calcium oxalate has been investigated as a protective surface treatment for limestone (Cezar 1998).

Synonyms and Related Terms

whewellite; weddellite; ethanedioic acid calcium salt


MFA- Calcium oxalate with organic component.jpg

Other Properties

Soluble in dilute mineral acids. Insoluble in water, acetic acid. Slightly hygroscopic.

Composition CaC2O4
CAS 5794-28-5
Melting Point 200C
Density 2.2
Molecular Weight mol. wt. = 128.1

Hazards and Safety

Contact may cause irritation. Ingestion is harmful.

Fisher Scientific: MSDS

Additional Information

° T.M. Cezar, "Calcium Oxalate: A Surface Treatment for Limestone" Journal of Museum Studies, No. 4, May 1988:

° M. del Monte, C. Sabbioni, G.Zappia. The origin of calcium oxalates on historical buildings, monuments and natural outcrops. The science of the total environment 67, (1987), pp. 17-39

° B. Ford, I.MacLeod, P.Haydock, "Rock art pigments from Kimberley region of Western Australia: identification of the minerals and conversion mechanisms." Studies in conservation 39, no. 1 (1994), pp. 57-69

The following sources were examined for information

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 1732

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