Monohydrocalcite

Monohydrocalcite is a mineral that is a hydrous form of calcium carbonate, CaCO₃.H₂O. It was formerly also known by the name hydrocalcite, which is now discredited by the IMA. It is a trigonal mineral which is white when pure. Monnohydrocalcite is not a common rock-forming mineral, but is frequently associated with other calcium and magnesium carbonate minerals, such as calcite, aragonite, lansfordite and nesquehonite.

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Monohydrocalcite has been observed in air conditioning systems, and as a deposit in caves, both probably formed from spray of carbonate rich fluids. It is well-known in the Robe in the Limestone Coast of South Australia as a component of beach sands of Lake Fellmongery and Lake Butler, where it is believed to be formed from algal spume. Other lacustrine deposits include Lake Issyk-Kul, Kyrgyzstan, Lake Kivu, Congo, and Solar Lake, Sinai.

It has been reported as a significant component of the decomposition of ikaite in the towers of the Ikka Fjord, West Greenland. It is also noted for its bizarre occurrences, which include inside the otoliths of the tiger shark, the bladder of a guinea pig, and the final stages of decomposition of the putrefying flesh of the giant saguaro cactus. These occurrences suggest a biochemical origin is possible.

Further reading

• Catherine, H., Skinner, K., Osbaldiston, G. W., Wilner, A. N. Monohydrocalcite in a guinea pig bladder stone, a novel occurrence. American Mineralogist, 62: 273 - 277, 1977.
• Dahl, K., Buchardt B. Monohydrocalcite in the arctic Ikka Fjord, SW Greenland:First reported marine occurrence. Journal of Sedimentary Research, 2006, vol. 76. DOI: 10.2110/jsr.2006.035
• Garvie, L.A.J. Decay-induced biomineralization of the saguaro cactus (Carnegiea gigantea) American Mineralogist, 88: 1879-1888, 2003
• Hull, H., Turnbull, A. G. A thermochemical study of monohydrocalcite. Geochimica et Cosmochimica Acta, 37: 685-694, 1973