mineral

Banded aragonite (often sold as banded calcite or “onyx marble”)

Aragonite, CaCO₃; commonly an aragonite–calcite carbonate aggregate

AI-generated identification · may be incorrect

Typically tan to brown with prominent cream bands, silky to pearly luster, and fibrous or layered crystal structure; Mohs hardness 3.5–4, with weak cleavage and specific gravity about 2.9. The specimen appears cut or naturally layered rather than tumbled.

Identified September 7, 2026More mineral →

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Physical properties

Formation & geological history

Forms by precipitation from carbonate-rich groundwater, hot springs, caves, or evaporitic systems; banding records changing impurities and growth conditions. Deposits are generally geologically young to Recent, though carbonate replacement can be older.

Uses & applications

Used as a decorative stone, carving material, ornamental specimen, and occasionally for interior surfaces; its softness limits heavy-duty construction use. Attractive pieces have modest collector value.

Geological facts

Aragonite is a polymorph of calcite: both have CaCO₃ but different crystal structures. Heating or burial may transform aragonite into calcite over geological time.

Field identification & locations

Identify by strong layered banding, carbonate reaction with dilute hydrochloric acid or vinegar, and softness—steel can scratch it. Common sources include Morocco, Spain, Mexico, Pakistan, and the western United States; avoid confusing it with banded calcite or travertine.