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.
But unlike most minerals, vaterite has defied every effort to resolve its crystal structure, stymieing scientists for nearly 100 years. The structure of a mineral crystal is a critically important feature and is determined by how atoms are arranged in the crystal. The arrangement of atoms and the resulting crystal structure, for instance, make the difference between graphite and diamond, both forms of pure carbon.
Now, however, a team of scientists from the Technion-Israel Institute of Technology and the University of Wisconsin-Madison has discovered the crystalline secrets of vaterite with the help of a needlelike spicule from a sea squirt found in the Mediterranean and Red Seas. Writing today (April 25, 2013) in the journal Science, a group led by Boaz Pokroy of Technion and Pupa Gilbert of UW-Madison report that vaterite is composed of two different crystal structures that “coexist within a pseudo-single crystal.”
Read more at: Phys.org