sedimentary
Chert (variations include Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Gray, tan, or black, Luster: Waxy to dull, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
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Physical properties
Hardness: 7 (Mohs), Color: Gray, tan, or black, Luster: Waxy to dull, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or the chemical replacement of limestone/dolomite by silica-rich fluids. Common in many sedimentary basins globally.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Today used as a component in construction aggregate, road base, and as a sparking device (flint and steel).
Geological facts
Chert breaks with a conchoidal fracture, creating razor-sharp edges which made it the primary material for prehistoric survival tools.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, curved fracture surfaces. Often found as nodules within limestone or as bedded layers in marine deposits.
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