mineral

Agate / Banded Chalcedony

Agate (Silicon Dioxide / SiO2)

Hardness: 6.5-7.0 (Mohs scale), Color: Banded white, tan, and dark blue/gray, Luster: Waxy to vitreous, Crystal structure: Trigonal (Microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6

Hardness: 6

Identified April 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities of volcanic rocks (basalt) or sedimentary rocks where silica-rich groundwater deposits successive layers of microcrystalline quartz over thousands of years.

Uses & applications

Used in gemstone jewelry (cabochons), ornamental carvings, industrial abrasive-resistant mortars and pestles, and as collected lapidary specimens.

Geological facts

The banding in agates is caused by the periodic deposition of silica during the growth of the crystal. This specific specimen shows 'fortification' style banding where the layers follow the shape of the original cavity.

Field identification & locations

Identify in the field by looking for a waxy luster on broken surfaces, translucent edges when held to light, and characteristic banding. Often found in riverbeds or gravel pits in volcanic regions.

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Mineral/Rock

Banded Gneiss (River Rock/Pebble)

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Metamorphic Rock

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