mineral

Agate

Silicon Dioxide (SiO2) - variety of Chalcedony

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Variegated with wavy bands of white, tan, and brown, Luster: Waxy to vitreous, Crystal Structure: Trigonal (cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.58-2.64

Hardness: 6

Identified February 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed as secondary deposits in cavities within volcanic or metamorphic rocks. Silica-rich groundwater fills gas vesicles (amygdales) or cracks, depositing microcrystalline quartz layers over thousands to millions of years.

Uses & applications

Commonly used in lapidary arts for jewelry, decorative carvings, bookends, and ornaments. Historically used for making precision bearings and mortars/pestles due to its hardness.

Geological facts

Agate bands are often so thin that a single inch can contain several thousand individual layers. It has been used as a gemstone for over 3,000 years, with some of the earliest recorded mining in the Achates River in Sicily.

Field identification & locations

Identify in the field by its translucent edges, waxy texture, and unique concentric or 'fortification' banding patterns. Frequently found in riverbeds, glacial till, or volcanic regions like the Lake Superior area, Brazil, and India.