sedimentary
Banded Chert (River Stone)
Silicon Dioxide (SiO2)
Hardness: 6.5-7.0 (Mohs scale), Color: layers of grey, tan, and brown, Luster: waxy to vitreous when polished, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture).
- Hardness
- 6
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Physical properties
Hardness: 6.5-7.0 (Mohs scale), Color: layers of grey, tan, and brown, Luster: waxy to vitreous when polished, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine environments; this specific specimen has been water-worn and polished in a river or beach setting.
Uses & applications
Historically used for stone tools and fire-starting; modern use includes rock tumbling, lapidary art, and decorative landscaping.
Geological facts
Chert is chemically identical to quartz but has a microcrystalline structure. Its sharp conchoidal fracture made it the primary material for arrowheads and scrapers for indigenous peoples globally.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its waxy texture, and its smooth, rounded river-worn shape. Commonly found in riverbeds and gravel pits.
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