Mineral

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

CaCO3 or CaF2 (depending on exact ID)

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 →

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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.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral