sedimentary
Banded Chert
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: Brownish-red bands in a greenish-tan matrix, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, SG: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-red bands in a greenish-tan matrix, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, SG: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation on the ocean floor, followed by burial and compaction into rock.
Uses & applications
Historically used for stone tools (arrowheads). Currently used for lapidary work (tumbled stones, cabochons), landscaping, and as a collector specimen.
Geological facts
Chert was a primary material for prehistoric toolmaking globally because it breaks with sharp edges. The distinct banding is often caused by variations in iron content during deposition.
Field identification & locations
Identify in the field by its waxy luster, conchoidal (shell-like) fracture, and inability to be scratched by a steel steel knife. Often found in riverbeds or coastal deposits.
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