mineral

Banded Agate (specifically sardonyx or carnelian agate variety)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Translucent white to tan with orange/red-brown concentric bands; Luster: Waxy to vitreous; Crystal structure: Trigonal/Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64

Hardness: 6
Luster: Waxy to vitreous

Identified March 22, 2026More mineral →

Explore Banded Agate (specifically sardonyx or carnelian agate variety) in the encyclopedia →

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Physical properties

Formation & geological history

Formed primarily in volcanic environments where silica-rich groundwater fills cavities (vesicles) in lava flows. Layering occurs through rhythmic deposition of silica over thousands of years. Age varies by tectonic region, often ranging from 10 to 100 million years old.

Uses & applications

Used widely in lapidary arts for jewelry, beads, and carvings. Historically used for making signet rings and cameos. In industry, it is used to make burnishers or mortars and pestles due to its hardness.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered. The 'eye' patterns sometimes found in these stones were historically believed to ward off the 'evil eye'. It is the birthstone for September and the 12th wedding anniversary stone.

Field identification & locations

Identify in the field by its distinct translucent concentric bands and waxy texture when wet. Commonly found in riverbeds, gravel pits, and coastal areas near ancient volcanic activity (e.g., Lake Superior region, Brazil, India). To collect, look for stones with a 'potato-skin' texture on the outside that reveal banding when chipped or sliced.