sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brown, grey, and rusty orange (iron staining), Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brown, grey, and rusty orange (iron staining), Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Forms through the accumulation of silica-rich microfossils or via chemical precipitation from silica-saturated groundwater within sedimentary layers. This water-worn pebble likely originated in a riverbed or coastal environment.
Uses & applications
Historically used for stone tools and strike-a-lights; currently used as decorative gravel, in lapidary work (polishing), and as industrial abrasives.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most vital materials for early humans because of its ability to break into sharp, durable edges called conchoidal fractures.
Field identification & locations
Identify in the field by its smooth, waxy feel and shell-like (conchoidal) breaks. It will not be scratched by a steel knife. Commonly found in riverbeds, gravel pits, and limestone formations.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Brecciated Chert (Microcrystalline Silica)
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