Search Mineralpedia – A Mineral Photo Database and Identification Guide
Named for an important industrial use of the mineral after the Latin word calx, or calce, for “lime.” Calcite is extremely common and widespread, and it is an important rock forming mineral and is common in limestone, marble, chalk, as a cement, hydrothermal veins, igneous rocks, and caves. Calcite is highly variable in color and forms, but it is most easily recognized by its reactivity to hydrochloric acid and even weaker acids like vinegar, which it will effervesce strongly when in contact with. Calcite can fluoresce red, blue, yellow, and many other colors and shades under both long-wave and short-wave ultraviolet light. It is also phosphorescent, cathodoluminescent, thermoluminescent and occasionally triboluminescent. Another telling property of Calcite is its strong optical birefringence which causes a double refraction, and thus double image, which can be viewed by looking at objects through a clear calcite specimen.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/calcite.pdf