mineral

Agate

Banded Chalcedony (SiO2)

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

Hardness: 6
Color: Multi-colored bands of brown, tan, yellow, and white
Luster: Waxy to vitreous

Identified May 30, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily within volcanic and metamorphic rocks or as nodules in sedimentary cavities. They originate when silica-rich groundwater fills cavities, depositing layers of microcrystalline quartz over thousands of years. Values for age range from the Precambrian to Cenozoic.

Uses & applications

Extensively used in jewelry (cabochons), interior decor (slices and bookends), precision pendulums, mortar and pestles for chemical testing, and widely collected as ornamental specimens.

Geological facts

Agate was named by the Greek philosopher Theophrastus after the Achates River in Sicily where it was first discovered. No two agates are identical, and the signature banding is due to alternating layers of chalcedony and opal.

Field identification & locations

Identified by its characteristic concentric or parallel banding and translucent appearance when held to light. Commonly found in Brazil, Uruguay, Germany, and Lake Superior in the USA. Collectors look for unique patterns and high-contrast color bands.