sedimentary
Chert (Flint)
Silicon dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 7 (Mohs scale), Color: Brown, tan, and grey with possible mottling, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown, tan, and grey with possible mottling, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (such as diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous to Paleozoic in age.
Uses & applications
Used historically for stone tools and weapons (arrowheads); currently used in road construction, stone mulch, and as an industrial abrasive or for fire-starting.
Geological facts
Chert breaks with a conchoidal fracture, creating extremely sharp edges. It is one of the most common materials used by early humans for lithic technology.
Field identification & locations
Identify in the field by its smooth, waxy surface where freshly broken and its ability to scratch glass. Commonly found as nodules in limestone outcrops or as rounded stream pebbles.
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