sedimentary
Black Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or chemical precipitation in sedimentary basins. The dark color often comes from organic matter trapped within the silica matrix.
Uses & applications
Historically used for stone tools/weapons (knapping) and fire-starting. Currently used as an abrasive, in road construction, and as a decorative stone.
Geological facts
The Western Caucasus region (near 43.4N, 40.0E) has significant limestone formations where chert nodules and flint are geologically common. This specimen shows a classic conchoidal fracture pattern and a light-colored weathered rind (cortex).
Field identification & locations
Identify by its ability to scratch glass and its distinctive sharp, curved fracture edges. Often found as nodules within limestone or as pebbles in riverbeds and along coastlines.
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