sedimentary

Banded Agate

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on the Mohs scale. Color: Brown, gray, white, and translucent layers. Luster: Waxy to vitreous. Structure: Trigonal (microcrystalline/cryptocrystalline quartz). Conchoidal fracture.

Hardness: 6
Color: Brown, gray, white, and translucent layers
Luster: Waxy to vitreous

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on the Mohs scale. Color: Brown, gray, white, and translucent layers. Luster: Waxy to vitreous. Structure: Trigonal (microcrystalline/cryptocrystalline quartz). Conchoidal fracture.

Formation & geological history

Formed as secondary deposits in cavities (vesicles) of volcanic or sedimentary rocks through the deposition of silica-rich groundwaters over millions of years. This process creates the characteristic concentric or parallel banding.

Uses & applications

Commonly used in jewelry, ornamental carvings, lapidary arts, and as a collector's specimen. Historically used for making precision burnishing tools because of its hardness.

Geological facts

The banding in agate is caused by the rhythmic precipitation of silica. No two agates are exactly alike, making each piece unique to collectors.

Field identification & locations

Identify in the field by looking for translucent edges, waxy surfaces, and concentric banding. Commonly found in riverbeds, gravel pits, and volcanic regions like the Lake Superior area in North America.