sedimentary
Banded Chert
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: tan, brown, orange, and gray bands, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brown, orange, and gray bands, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. These specimens often form as nodules or beds within limestone or dolostone.
Uses & applications
Historically used for stone tools and arrowheads due to its conchoidal fracture. Modern uses include decorative lapidary work, landscaping, and as a source of silica.
Geological facts
Banded chert can sometimes contain microfossils. It is extremely chemically stable and resistant to weathering, which is why it often survives as smooth river stones or high-relief outcrops.
Field identification & locations
Identify by its banded appearance, waxy texture, and sharp edges when broken. Frequently found in riverbeds, glacial till, and sedimentary basins worldwide.
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