sedimentary
Banded Calcite (often marketed as 'Mexican Onyx')
Calcite (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Creamy white with tan, brown, and translucent banding; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific gravity: 2.71
- Hardness
- 3 on Mohs scale
- Color
- Creamy white with tan, brown, and translucent banding
- Luster
- Vitreous to waxy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3 on Mohs scale; Color: Creamy white with tan, brown, and translucent banding; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific gravity: 2.71
Formation & geological history
Formed through the precipitation of calcium-rich water in caves or around hot springs (travertine), often as flowstone or dripstone. These specimens are typically from the Quaternary period.
Uses & applications
Used primarily for ornamental carvings, decorative beads, household items like chess sets or bookends, and architectural interior cladding.
Geological facts
Despite the trade name 'Onyx,' it is NOT true onyx (which is a form of chalcedony/quartz). This material is much softer and can be dissolved by weak acids like vinegar.
Field identification & locations
Identify in the field by its distinct parallel layering and extreme softness (it can be scratched by a copper penny or steel knife). It is commonly found in Mexico, Turkey, and Pakistan. Collectors should check for a 'waxy' translucent feel.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary