Vaterite: Crystal Within a Crystal Helps Resolve an Old Puzzle

With the help of a solitary sea squirt, scientists have resolved the longstanding puzzle of the crystal structure of vaterite, an enigmatic geologic mineral and biomineral. 

A form of calcium carbonate, vaterite can be found in Portland cement. Its quick transformation into other more stable forms of calcium carbonate when exposed to water helps make the cement hard and water resistant. As a biomineral, vaterite is found in such things as gallstones, fish otoliths, freshwater pearls, and the healed scars of some mollusk shells.  

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Just 10 micrometers in diameter, the needlelike spicule from the sea squirt Herdmania momus helped researchers in Israel and Wisconsin unlock the crystal structure of vaterite, a geologic and biogenic mineral whose structural secrets have stymied scientists for almost 100 years. (Credit: Pupa U. P. A. Gilbert, Lee Kabalah-Amitai, Boaz Pokroy)

Credit: http://www.news.wisc.edu