sedimentary
Chert (Commonly known as Flint or River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brown, tan, and grey, 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: Brown, tan, and grey, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich microfossils or chemical precipitation in sedimentary basins. This water-worn pebble suggests a period of erosion and transport in a fluvial (river) environment.
Uses & applications
Historically used for stone tools and fire-starting. Currently used in road construction, landscaping, and as decorative river stones. High silica content makes it useful in glassmaking.
Geological facts
Chert is so hard it can scratch steel. It was the primary material for spearheads and arrowheads for thousands of years due to its predictable, razor-sharp conchoidal fracture.
Field identification & locations
Identify by its smooth, waxy texture and extreme hardness. Look for it in riverbeds, glacial tills, or limestone outcrops. It often shows a yellowish-brown 'cortex' or weathering rind.
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