sedimentary
Banded Calcite
CaCO3
AI-generated identification · may be incorrectMohs hardness of 3, white to tan/brown colors, vitreous to pearly luster, rhombohedral crystal structure, perfect cleavage in three directions.
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Physical properties
Mohs hardness of 3, white to tan/brown colors, vitreous to pearly luster, rhombohedral crystal structure, perfect cleavage in three directions.
Formation & geological history
Forms in sedimentary environments, often deposited by mineral-rich waters in caves or hot springs as travertine or tufa.
Uses & applications
Carved into decorative objects, bookends, and polished stones; used historically in sculpture.
Geological facts
Often mislabeled commercially as 'Onyx' (e.g., 'Mexican Onyx'), which is technically a variety of quartz (chalcedony), whereas this is softer calcite.
Field identification & locations
Identify by its banding, softness (can be scratched by a knife or coin), and effervescence with weak acid. Commonly found in Mexico, Pakistan, and the USA.
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