mineral

Tumbled banded calcite (often sold as “onyx” or green onyx)

Calcite, CaCO₃; commonly banded cave/travertine calcite

AI-generated identification · may be incorrect

Typically pale green to cream with parallel translucent bands, vitreous to pearly luster, and a smooth tumbled surface. Mohs hardness 3, rhombohedral crystal structure, perfect rhombohedral cleavage, and specific gravity about 2.71; effervesces in dilute hydrochloric acid.

Identified August 8, 2026More mineral →

Explore Tumbled banded calcite (often sold as “onyx” or green onyx) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when calcium-carbonate-rich groundwater precipitates in caves, springs, or hot-spring deposits, producing layered bands. The specimen is likely a polished/tumbled piece rather than a natural crystal; its exact geological age cannot be determined from the image.

Uses & applications

Used as a decorative stone, carvings, polished specimens, and occasionally countertops or interior ornament; it is generally unsuitable for durable jewelry because it scratches easily.

Geological facts

Commercial “green onyx” is usually banded calcite, not true onyx (a variety of chalcedony). Its translucent bands and acid reaction distinguish it from glass and many similarly colored stones.

Field identification & locations

Common sources include Mexico, Pakistan, Turkey, and Argentina. Identify by its softness, banding, cleavage, and acid fizz; avoid prolonged water or acidic cleaners.