sedimentary
Chert / Flint Nodule
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: Dark grey, charcoal to brown, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey, charcoal to brown, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the precipitation of silica in sedimentary environments, often replacing calcium carbonate in limestone or chalk beds. It can date from the Precambrian to recent times, frequently found in Cretaceous deposits.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges; used in industrial grinding media, road construction, and fire-starting (flint and steel).
Geological facts
Chert was one of the most vital raw materials for early humans; when struck, it breaks with a conchoidal fracture that creates edges sharper than a surgical scalpel. It is chemically identical to quartz but has a different microscopic structure.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth waxy feel on broken surfaces, and the way it rings slightly when struck. Commonly found in riverbeds or eroding out of limestone cliffs.
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