mineral

Banded Agate (specifically Carnelian Agate / Sardonyx)

Silicon Dioxide (SiO2) with iron oxide inclusions

Hardness: 6.5-7 on Mohs scale. Color: Layers of reddish-brown (sard), orange (carnelian), and black/white. Luster: Vitreous to waxy. Crystal structure: Hexagonal (rhombohedral) cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.64.

Hardness: 6
Luster: Vitreous to waxy

Identified March 11, 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 the deposition of silica from groundwater in the cavities of igneous rocks such as basalt. The banding represents discrete stages of mineral precipitation over thousands of years. Often found in volcanic regions dating back to the Triassic and Jurassic periods.

Uses & applications

Extensively used in lapidary arts for jewelry, cameos, and carvings. Historically used for signet rings and seals because hot wax does not stick to it. Also used in industry for precision mortars and pestles due to its hardness.

Geological facts

In ancient times, Sardonyx was believed to grant its wearer courage and eloquence. It is one of the oldest gemstones used by humans, with evidence of its use in Crete and Mesopotamia dating back over 4,000 years. It is a traditional birthstone for August.

Field identification & locations

Identify in the field by its distinct parallel banding (fortification lines), waxy texture when broken, and inability to be scratched by a steel knife. Common locations include Brazil, India, Uruguay, and the Lake Superior region of the USA.

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