mineral

Agate

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Banded grey, white, red, and translucent layers; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Color: Banded grey, white, red, and translucent layers
Luster: Waxy to vitreous

Identified May 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in volcanic rock cavities (vesicles) where silica-rich groundwater deposits layers over thousands of years. Often found in nodules within basalt or as part of sedimentary deposits.

Uses & applications

Commonly used in jewelry (cabochons), lapidary art, decorative ornaments, and historically for precision tools like mortars and pestles due to its hardness.

Geological facts

The name Agate comes from the Achates River in Sicily. It is distinctive for its 'fortification' banding patterns, which represent periodic changes in the silica concentration during formation.

Field identification & locations

Identify in the field by its waxy luster, translucency when held to light, and characteristic concentric banding. Frequently found in gravel beds or near volcanic formations in regions like Brazil, India, and the United States (Lake Superior region).