mineral

Sardonyx

Silicon Dioxide (SiO2) with iron oxide impurities

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown with white/black bands; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Reddish-brown with white/black bands
Luster: Vitreous to waxy

Identified June 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica in gas cavities of volcanic rocks, often resulting in distinct parallel bands. Typically found in hydrothermal environments.

Uses & applications

Commonly used in jewelry (rings, pendants), carvings such as cameos and intaglios, and popular in crystal healing and gemstone collecting.

Geological facts

Sardonyx was highly popular in Ancient Rome for making signet rings and seals because hot wax does not stick to it. It has been used for over 4,000 years.

Field identification & locations

Identify by its distinct parallel bands of sard (reddish-brown) and onyx (white or black). Regularly found in Brazil, India, Germany, and Uruguay.

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

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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