sedimentary
Chert (Common Jasper/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brown, tan, and gray mottled, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown, tan, and gray mottled, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include jewelry (jasper), landscaping, and as a raw material for silicon production.
Geological facts
Chert was one of the first materials used by early humans to create sharp tools because it breaks with predictable, razor-sharp conchoidal fractures.
Field identification & locations
Identify by its hardness (it will scratch glass) and its characteristic smooth, bowl-shaped fractures. Often found in riverbeds or as nodules protruding from sedimentary rock outcrops.
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