sedimentary
Chert Pebble
Microcrystalline silica (SiO2)
Hardness: 7 (Mohs scale), Color: Gray/brown, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific gravity: 2.5-2.8
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Physical properties
Hardness: 7 (Mohs scale), Color: Gray/brown, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific gravity: 2.5-2.8
Formation & geological history
Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous organisms like diatoms and radiolarians; often found as nodules in limestone.
Uses & applications
Historically used for stone tools (arrowheads); currently used in road construction, as decorative gravel, and as a component in various manufacturing processes.
Geological facts
Chert is essentially high-purity quartz with microscopic crystals. It is very durable and chemical-resistant, which is why it often survives as rounded pebbles in riverbeds and on beaches.
Field identification & locations
Identify by its hardness (will scratch glass), waxy appearance, and conchoidal (shell-like) fracture patterns. Found globally in alluvial deposits and sedimentary basins.
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