SEPM Strata


calcite
igneous rocks metamorphic rocks minerals sedimentary rocks	Description This is a typical specimen of calcite showing the perfect Rhombohedral Cleavage (multiple cleaves through the specimen), clear to slightly gray color, and vitreous (glassy) luster. There are, however, many variations on calcite so you must be alert for the defining physical properties, which are the rhombohedral cleavage and reaction with dilute hydrochloric acid. Physical Properties CaCO₃; hardness 3; Cleavage Rhombohedral; hydrochloric acid reaction; white, colorless, pale shades of gray, yellow, red, green, blue; Luster vitreous (glassy) Another Sample Description Here we are looking down on top of the calcite to see the rhombohedral cleavage. Note also the white color of this specimen, and its transluscence. Detail Description Here we see a common condition, calcite not as a single crystal, but as a mass of intergrown crystals randomly oriented. The cleavage is clearly here, but unless you isolate one crystal you will have trouble identifying it as rhombohedral. Can you pick out the different crystals present? Can you find a good example of the rhombohedral cleavage? Further Detail Description A more difficult view. Can you see the cleavage? Can you positively identify it as rhombohedral? If you cannot, then how else might you identify this specimen?