sedimentary
Chert (often called Flint or River Pebble)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale), Color: Brown/earthy tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown/earthy tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine or groundwater environments. This specific specimen appears water-worn, likely from a fluvial (river) environment.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a durable material for stone tumbling/polishing.
Geological facts
Chert is so hard it can scratch glass. Because of its conchoidal fracture (breaking like glass with sharp edges), it was the primary material for prehistoric arrowheads and scrapers.
Field identification & locations
Identify in the field by its extreme hardness, waxy texture when broken, and lack of visible grains. Common in riverbeds and limestone outcrops.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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