mineral

Banded Agate

Chalcedony (Silicon Dioxide, SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Banded orange, reddish-brown, and white, Luster: Vitreous to waxy, Crystal Structure: Trigonal (Microcrystalline), Cleavage: None, Fracture: Conchoidal.

Hardness: 6

Identified July 1, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Banded orange, reddish-brown, and white, Luster: Vitreous to waxy, Crystal Structure: Trigonal (Microcrystalline), Cleavage: None, Fracture: Conchoidal.

Formation & geological history

Formed primary in volcanic rocks when silica-rich fluids fill cavities or gas bubbles (vesicles), depositing layers of chalcedony over time. These specimens are often found in gravel deposits and riverbeds.

Uses & applications

Used in jewelry (cabochons, beads), decorative carvings, and as a popular collector's stone. Historically used for making mortars and pestles due to its hardness.

Geological facts

The banding in agate is caused by the rhythmic crystallization of silica. No two agates are exactly alike, making each piece unique. It is the state gemstone of several US states, including Minnesota (Lake Superior Agate).

Field identification & locations

Identify in the field by looking for translucent edges, waxy texture when wet, and characteristic concentric or parallel banding pattern. Commonly found in areas with past volcanic activity or in glacial till.