mineral

Agate

Chalcedony (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, white with banded patterns; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Tan, brown, white with banded patterns
Luster: Waxy to vitreous

Identified February 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in volcanic and metamorphic rocks as silica-rich groundwater fills cavities (vesicles) or cracks, depositing quartz in layers over thousands to millions of years. Common in Cenozoic deposits.

Uses & applications

Used in jewelry, decorative ornaments, mortar and pestle for laboratories, and precision bearings for mechanical instruments due to its hardness.

Geological facts

Agates are often named after their location or appearance, such as Lake Superior Agate or Moss Agate. They have been used by humans for over 3,000 years, beginning with the ancient Greeks.

Field identification & locations

Identified by its waxy luster when wet, translucent edges when held to light, and characteristic concentric banding. Frequently found in riverbeds, glacial till, and gravel pits across North America.