sedimentary
Chert (Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: light to dark gray with subtle banding, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6
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Physical properties
Hardness: 7 (Mohs scale), Color: light to dark gray with subtle banding, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6
Formation & geological history
Formed as chemical precipitates or through the replacement of limestone by silica-rich fluids. Often found as nodules or layers in marine sedimentary rocks, weathered out and rounded by water action.
Uses & applications
Historically used for stone tools (flint); currently used in road construction, landscaping, and as a durable material for rock tumbling.
Geological facts
Chert is a tough, durable rock that often preserves microfossils. When broken, it produces sharp edges, which led to its widespread use by prehistoric humans for arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy luster, and conchoidal (shell-like) fracture. Commonly found in riverbeds, beaches, and eroded out of limestone cliffs.
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