Not Your Typical Gallstone

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Science  09 May 2003:
Vol. 300, Issue 5621, pp. 867
DOI: 10.1126/science.300.5621.867d

Vaterite is a CaCO3 polymorph that tends to form spherules and is most painfully familiar to some as gallstones. Inorganic vaterite is rarely found on Earth and has never been conclusively found to precipitate from natural waters.

Grasby has found vaterite precipitating inorganically from supraglacial sulfur-rich natural spring waters in Borup Fiord Pass, Ellesmere Island, in the Canadian High Arctic. Vaterite precipitation is favored because the water is extremely cold (1° to 2°C) and highly alkaline (pH 7.3 to 9.5). Sulfate-reducing bacteria are active in these springs, making the competing process of methanogenesis, which might yield organic vaterite, unlikely. Understanding how vaterite forms in this extreme biogenic environment can help to explain carbonate precipitation under different conditions and provides clues about terrestrial extremophiles and their biomarkers, and perhaps useful analogs for other planetary environs. Groundwater discharges at Borup Fiord Pass are similar to suggestions of liquid water discharges on Mars and perhaps Europa. The carbonate spherules in the Martian meteorite ALH 84001, considered possible evidence for life, are similar in shape to the vaterite, although the Martian carbonates are rich in Mg and Fe, making any additional correlation inconclusive.—LR

Geochim. Cosmochim. Acta 67, 1659 (2003).

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