sedimentary

Banded Onyx (Calcite Marble)

Calcite (CaCO3) - Trap-rock or Cave Onyx

Hardness: 3 on Mohs scale; Color: Multi-colored bands of gold, cream, grey, and black; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: Multi-colored bands of gold, cream, grey, and black
Luster: Vitreous to waxy

Identified March 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of calcium carbonate from cold water springs or within limestone caves as dripstone. While the limestone bedrock may be millions of years old, these flowstone formations are often Quaternary in age.

Uses & applications

Extensively used for ornamental carvings, interior countertops, decorative tiles, bookends, and low-cost jewelry beads.

Geological facts

Commercial 'Onyx' is often actually a form of banded calcite or travertine. True geological onyx is a variety of chalcedony (quartz), which is much harder (7 on Mohs scale) than this specimen.

Field identification & locations

Identify by its translucent nature when sliced thin and its reaction (fizzing) to weak acids like vinegar. Commonly found in Mexico, Pakistan, Iran, and Turkey. Collectors should look for distinct, vibrant parallel banding.

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