sedimentary
Chert (Flint)
Chert (Microcrystalline Silicon Dioxide, SiO2)
Hardness: 7 Mohs, Color: Light grey to white with variations, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 Mohs, Color: Light grey to white with variations, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed by the precipitation of silica from seawater or the accumulation of siliceous skeletal remains (like diatoms or radiolarians). Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and fire-starting. Currently used in road surfacing, as grinding media, and occasionally in jewelry as cabochons.
Geological facts
Chert is so hard it can scratch steel. When broken, it produces extremely sharp edges, which is why it was the primary material for prehistoric arrowheads and spear points.
Field identification & locations
Identify by its smooth, waxy surface and its characteristic 'shell-like' conchoidal fracture. Common in sedimentary basins worldwide.
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