metamorphic
Polished onyx marble (banded calcite)
Calcite, CaCO₃; commonly called Mexican onyx or cave onyx
AI-generated identification · may be incorrectTypically Mohs hardness 3, specific gravity about 2.6–2.8, vitreous to pearly luster, and translucent cream, tan, brown, or green banding. It has rhombohedral calcite cleavage and reacts strongly with dilute acid; the circular piece is polished and cut.
Identified More metamorphic →
Explore Polished onyx marble (banded calcite) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically Mohs hardness 3, specific gravity about 2.6–2.8, vitreous to pearly luster, and translucent cream, tan, brown, or green banding. It has rhombohedral calcite cleavage and reacts strongly with dilute acid; the circular piece is polished and cut.
Formation & geological history
Despite its name, this is usually banded calcite formed by precipitation from mineral-rich groundwater in caves, springs, or hydrothermal settings; it is not true silica onyx. Deposits are generally geologically young compared with bedrock, often Quaternary to Tertiary.
Uses & applications
Used for decorative slabs, tabletops, tiles, carvings, and ornamental specimens; softer and less durable than quartz onyx, so it is unsuitable for heavy-wear flooring or exposed exteriors.
Geological facts
The rhythmic bands record changing water chemistry and flow conditions during successive mineral-deposition episodes. Backlighting can reveal attractive translucency.
Field identification & locations
Identify it by cream-to-brown translucent bands, very low hardness, and vigorous acid effervescence; common sources include Mexico, Pakistan, Turkey, Iran, and the United States. Avoid vinegar or acid testing on valuable polished pieces.
More like this
