mineral

Agate

Silicon Dioxide (SiO2)

Hardness: 6.5–7 on the Mohs scale. Color: Highly variable (white, grey, blue, orange, red, brown) often in concentric bands. Luster: Waxy to vitreous. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified January 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed as secondary deposits in volcanic rock cavities (vugs) or ancient lavas through the rhythmic precipitation of silica from groundwater. Most specimens range from a few million to over a billion years old depending on the host rock formation.

Uses & applications

Used extensively in jewelry (cabochons, beads), decorative lapidary arts, and ornamental carvings. Historically used for making precision bearings, mortar and pestles, and seal stones.

Geological facts

Famous varieties include Lake Superior Agate, Botswana Agate, and Fire Agate. It was named by the Greek philosopher Theophrastus after the Achates River in Sicily where he first discovered it around the 4th century B.C.

Field identification & locations

Identify in the field by its distinctive waxy texture and characteristic color banding when broken. It is often found as nodules inside volcanic host rocks or as loose river stones. Common locations include Brazil, Uruguay, Germany, and the United States (specifically Lake Superior and the Pacific Northwest).