The calcite group of minerals includes calcite, magnesite, siderite, rhodochrosite, smithsonite, and the high-pressure polymorph aragonite. Calcite is the primary mineral in limestone, chalk and marble, and forms the stalagtites and stalagmites in caves.
Pronunciation: CAL•site (accent on capitalized syllable)
Color: highly variable to colorless
Luster: vitreous
Diaphaneity: transparent to translucent; may appear opaque in hand specimen
Hardness: 3
Specific gravity: 2.71
Cleavage/fracture: 3 at oblique angles to one another, forming a "squashed box"
Other distinguishing properties: Calcite effervesces (fizzes) easily in dilute hydrochloric acid (or vinegar). Its cleavage rhombs look like "squashed boxes."
Klein, C., and Hurlbut, C.S., Jr., 1999, Manual of Mineralogy (after James D. Dana) [21st edition, revised]: New York, John Wiley & Sons, 682 p.
Los Angeles County Museum of Natural History, The Photo Atlas of Minerals: nhm.org/pam/
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