Mineral

Banded Calcite / Fluorite (or Onyx/Agate depending on hardness)

CaCO3 or CaF2 (depending on exact ID)

AI-generated identification · may be incorrect

Translucent, banded, vitreous luster. If calcite: Mohs hardness 3, perfect rhombohedral cleavage. If fluorite: Mohs hardness 4, octahedral cleavage. Colors can range from white, cream, brown, to dark grey/black.

Identified June 19, 2026More mineral →

Explore Banded Calcite / Fluorite (or Onyx/Agate depending on hardness) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through precipitation from aqueous solutions, often in veins or hot spring deposits. Can form over various geological periods.

Uses & applications

Often used for carving, lapidary arts, ornamental objects, and jewelry (cabochons, pendants).

Geological facts

Banded varieties are sometimes commercially sold as 'onyx' or 'marble' in the lapidary trade, though geologically they are often banded calcite.

Field identification & locations

Identify by hardness testing (can it be scratched by a steel nail?), acid test (effervesces with drop of dilute HCl if calcite), and banding patterns.