mineral

Agate

Silicon Dioxide (SiO2) - variety: Chalcedony

Hardness: 6.5–7 on Mohs scale; Color: Multi-colored bands (white, brown, tan); Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline/Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64

Hardness: 6
Color: Multi-colored bands (white, brown, tan)
Luster: Waxy to vitreous

Identified April 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities of volcanic or sedimentary rock through the slow deposition of silica-rich groundwater. Over long periods, varying mineral impurities create the distinct concentric bands.

Uses & applications

Used in lapidary art, jewelry, interior decor (bookends, coasters), and historically for precision mechanical components like scale bearings due to its hardness.

Geological facts

The name 'Agate' comes from the Achates River (now Dirillo) in Sicily. It is one of the oldest gemstones used in human history, dating back to Babylon and Ancient Egypt for amulets.

Field identification & locations

Identify in the field by its translucency when held to light and its characteristic 'fortification' banding. Often found as nodules in riverbeds or volcanic regions like the American Northwest, Brazil, and India.