mineral
Banded Agate / Chalcedony
Cryptocrystalline Quartz (SiO2)
Mohs hardness of 6.5 to 7. Color ranges from tan, brown, beige, to reddish shades with wavy banding and tiny druzy quartz pockets. Luster is waxy to vitreous. Trigonal crystal system (microcrystalline). Specific gravity around 2.58–2.64.
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Physical properties
Mohs hardness of 6.5 to 7. Color ranges from tan, brown, beige, to reddish shades with wavy banding and tiny druzy quartz pockets. Luster is waxy to vitreous. Trigonal crystal system (microcrystalline). Specific gravity around 2.58–2.64.
Formation & geological history
Forms primarily as secondary deposits in volcanic rocks or limestone cavities. Silica-rich hydrothermal fluids precipitate silica layer by layer inside gas vesicles or fractures, creating distinct banding patterns.
Uses & applications
Popular among rockhounds for tumbling, cabochon cutting, lapidary art, and jewelry. Used historically for amulets and carvings.
Geological facts
Agate bands can be as thin as a few micrometers. The intricate layering records fluctuations in chemical composition during fluid deposition millions of years ago.
Field identification & locations
Identified by its distinctive concentric or parallel microcrystalline silica bands, waxy texture, and high hardness (will scratch glass). Commonly found in river beds, beaches, and weathered volcanic basalt fields worldwide.
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