mineral

Agate

Silicon Dioxide (SiO2) - variety Chalcedony

Hardness: 6.5–7 (Mohs scale); Color: Translucent tan, brown, and grey with possible banding; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58–2.64

Hardness: 6
Color: Translucent tan, brown, and grey with possible banding
Luster: Waxy to vitreous

Identified March 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed as secondary deposits in volcanic rock cavities (vesicles) or sedimentary rock. Silica-rich water percolates through voids, depositing layers of microcrystalline quartz over thousands of years.

Uses & applications

Commonly used for ornamental carvings, jewelry (cabochons), burnishing tools, mortar and pestles due to its hardness, and as collector display pieces.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered. Every agate specimen is technically unique due to the specific mineral impurities and layer timing during its formation.

Field identification & locations

Identify in the field by its waxy texture, translucency when held to light, and characteristic conchoidal (shell-like) fracture. Commonly found in riverbeds, or on beaches such as the Great Lakes or the Pacific Northwest.