sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to brown/tan banding, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to brown/tan banding, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the precipitation of silica-rich fluids in sedimentary environments or the accumulation of microscopic silica-shelled organisms. This specific stream-weathered pebble likely dates from variable geological eras depending on location.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include landscaping, road gravel, and sometimes as a minor gemstone when polished (lapidary).
Geological facts
Chert has a unique property where it breaks into very sharp edges, making it the primary material for prehistoric survival tools globally. It is chemically identical to quartz but has a much finer grain structure.
Field identification & locations
Identify by its hardness (scratches glass), smooth waxy feel, and curved 'conchoidal' fracture lines. Commonly found in riverbeds, glacial deposits, and sedimentary basins worldwide.
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