Geologic or synthetic mineral crystals usually have flat faces and sharp edges, whereas biomineral crystals can have strikingly uncommon forms that have evolved to enhance function. The image here was captured using environmental scanning electron microscopy and false-colored. Each color highlights a continuous single-crystal of calcite (CaCO3) made by the sea urchin Arbacia punctulata, at the forming end of one of its teeth.
Image credit: Pupa U.P.A. Gilbert and Christopher E. Killian, University of Wisconsin-Madison