sedimentary
Polished banded calcite (often sold as “onyx marble” or Mexican onyx)
Banded calcite, CaCO₃ (sometimes aragonite); decorative “onyx marble” is not true quartz onyx
AI-generated identification · may be incorrectCream, tan, gray, and dark wavy bands with a polished luster; calcite is Mohs 3, rhombohedral, and has perfect cleavage. The image shows a carved, polished point; mineral composition cannot be confirmed visually.
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Physical properties
Cream, tan, gray, and dark wavy bands with a polished luster; calcite is Mohs 3, rhombohedral, and has perfect cleavage. The image shows a carved, polished point; mineral composition cannot be confirmed visually.
Formation & geological history
Typically precipitates from calcium-rich groundwater in caves or springs, forming layered travertine/cave calcite over time; often Quaternary to recent, though deposits vary in age.
Uses & applications
Used for carved ornaments, bookends, and interior decoration; softer and less durable than quartz or granite.
Geological facts
Despite the trade name “onyx,” this material is commonly calcite rather than silica-based chalcedony.
Field identification & locations
Look for translucent, flowing bands and test hardness or acid reaction on an inconspicuous spot: calcite scratches readily and fizzes with dilute acid. Similar material is quarried in Mexico, Pakistan, and other regions.
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