Magazine article Science News

Calcite on the Edge of Growth, Dissolution

Magazine article Science News

Calcite on the Edge of Growth, Dissolution

Article excerpt

Wheter incorporated into seashells or deposited as limestone, marble or chalk, the mineral calcite participates in a variety of biological and geologic processes. To help elucidate how calcite fulfills it svaried roles, researchers have developed a new technique for observing hitherto hidden details of the way calcite crystallizes and dissolves.

Physics graduate student Paul E. Hillner of the University of California, Santa Barbara, geoscientist Andrew J. Gratz of the Lawrence Livermore (Calif.) National Laboratory and their co-workers use an atomic force microscope to observe the step-by-step addition or removal of calcium and carbonate ions at a calcite crystal surface. Although they can't detect individual atoms, they can clearly see the apparent movement of edges as ions settle into layers to produce characteristic patterns of steps.

These findings represent "extremely important first observations [by atomic force microscopy] of in situ crystal growth ... of a mineral," comments Richard J. Reeder of the State University of New York at Stony Brook, who has also studied calcite growth.

Hillner and his colleagues describe their work in the April GEOLOGY.

The researchers track changes in surface features during crystal growth by passing a concentrated solution of calcium carbonate dissolved in water across the surface of a calcite sample. By making the solution highly alkaline, they slow the deposition process sufficiently to allow time for repeatedly scanning the surface to detect any changes. …

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