mineral

Aragonite (Onyx Marble)

Aragonite / Calcium Carbonate (CaCO3)

Hardness: 3.5-4.0 on Mohs scale. Color: Pale green with tan/brown banded inclusions. Luster: Vitreous to pearly. Crystal Structure: Orthorhombic. Cleavage: Distinct in one direction. Specific Gravity: 2.9–3.0.

Hardness: 3
Color: Pale green with tan/brown banded inclusions
Luster: Vitreous to pearly

Identified March 17, 2026More mineral →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed through biological and physical processes, including precipitation from marine and freshwater environments. Commonly found in hot springs, karst caves (as flowstone), and mollusk shells. This specimen appears to be banded travertine or 'Mexican Onyx'.

Uses & applications

Used primarily for ornamental purposes such as carvings, jewelry, interior decoration (tiles and countertops), and as lapidary rough for cabochons.

Geological facts

Despite being called 'Onyx' in the trade, it is chemically different from true Onyx (which is chalcedony). Aragonite is metastable and can recrystallize into calcite over millions of years at surface temperatures and pressures.

Field identification & locations

Identify by its waxy luster and reaction to dilute hydrochloric acid (it will fizz). Look for banding and translucency. Found globally in limestone deposits, particularly in Mexico, Morocco, and Italy.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

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

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral