sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-gray with dark patches, Luster: Dull/Waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-gray with dark patches, Luster: Dull/Waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed by the precipitation of silica from groundwater filling voids in sedimentary rock or from the accumulation of siliceous microfossils. This specimen shows signs of fluvial erosion (rounded by water).
Uses & applications
Used historically for stone tools due to its sharp edges; used today as construction aggregate, road base, and occasionally as decorative landscaping stone.
Geological facts
Chert is one of the most durable rocks and can survive long-distance transport in rivers. It was the primary material for arrowheads and scrapers used by early humans.
Field identification & locations
Identified by its high hardness (it can scratch glass), waxy luster when fresh, and smooth rounded surface from water wear. Commonly found in riverbeds and gravel pits.
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