Mineral / Sedimentary Rock
Banded Calcite (often sold as 'Mexican Onyx')
Calcite (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, tan, and dark grey banding; Luster: Vitreous to waxy when polished; Crystal structure: Trigonal; Specific gravity: 2.71
- Hardness
- 3 on Mohs scale
- Color
- Cream, tan, and dark grey banding
- Luster
- Vitreous to waxy when polished
Identified More mineral / sedimentary rock →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3 on Mohs scale; Color: Cream, tan, and dark grey banding; Luster: Vitreous to waxy when polished; Crystal structure: Trigonal; Specific gravity: 2.71
Formation & geological history
Formed through the precipitation of calcium carbonate from cold spring water or groundwater in caverns. This specimen likely originates from the Tehuacán region of Mexico, formed during the Cenozoic era.
Uses & applications
Primarily used for decorative carvings, figurines, bookends, and interior design elements due to its softness and ability to take a high polish.
Geological facts
Despite the trade name 'Onyx,' this material is actually calcite. True onyx is a variety of chalcedony (quartz) and is much harder (7 on the Mohs scale).
Field identification & locations
Identify in the field by its distinctive parallel banding and extreme softness (can be scratched by a copper penny or steel knife). It will react and 'fizz' strongly when exposed to weak hydrochloric acid or vinegar.
More like this
Other mineral / sedimentary rock specimens
Quartz Geode (partially formed/chalcedony with iron staining)
Quartz (SiO2) with Chalcedony (cryptocrystalline quartz) and likely Iron Oxides/Hydroxides
Mineral/Sedimentary Rock Feature
Banded Jasper
Silicon Dioxide (SiO2)
Mineral/Sedimentary Rock (as a cryptocrystalline variety of quartz)
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
River Rock / Stream Pebble
Fluvial Clast / Rounded Sedimentary Particle
Sedimentary Rock (possibly composed of various minerals)
Shale (Beach-worn)
Laminated Pelite (primarily clay minerals and quartz)
sedimentary
Shale
Lutaceous sedimentary rock
sedimentary