sedimentary
Chert (White Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: White to off-white, Luster: Waxy to dull, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: White to off-white, Luster: Waxy to dull, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. It occurs as nodules or beds in limestone or chalk formations.
Uses & applications
Historically used for stone tools and arrowheads; today used in construction as aggregate, in ceramics, and occasionally as a gemstone in jewelry (when colored).
Geological facts
Chert has been a vital material for humans for millions of years due to its ability to break with razor-sharp edges. It is chemically identical to quartz but has a much finer grain structure.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth waxy feel, and characteristic shell-like (conchoidal) fracture lines when broken. Common in riverbeds and limestone outcrops.
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