sedimentary
Chert (Jasper/Flint variety)
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: tan, brownish-orange, Luster: waxy to dull, Structure: cryptocrystalline, Fracture: conchoidal, Specific Gravity: approx. 2.6
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brownish-orange, Luster: waxy to dull, Structure: cryptocrystalline, Fracture: conchoidal, Specific Gravity: approx. 2.6
Formation & geological history
Formed from the recrystallization of silica-rich marine sediments or chemical precipitation from groundwater within other sedimentary rocks. Often found in nodules within limestone or chalk.
Uses & applications
Historical use for stone tools and fire-starting (flint); modern uses include landscaping gravel, abrasive materials, and occasionally as a semi-precious gemstone (jasper).
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture allows it to be broken into razor-sharp edges for arrowheads and scrapers.
Field identification & locations
Identifiable by its smoothness, waxy luster, and sharp edges when broken. Look for it in riverbeds or within limestone outcrops. It will easily scratch glass.
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