sedimentary
Chert (Nodule)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brown/Dull tan, Luster: Waxy to dull, Crystal structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown/Dull tan, Luster: Waxy to dull, Crystal structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed in sedimentary environments through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds. Often found as nodules.
Uses & applications
Historically used for stone tools (arrowheads). Currently used as road aggregate, in jewelry (when polished), or as a grinding medium.
Geological facts
Chert is so hard it can scratch steel and was used for centuries to spark fires. It is one of the most common materials for prehistoric stone tools due to its predictable fracturing.
Field identification & locations
Identify by its extreme hardness, smooth waxy texture, and seashell-like conchoidal fractures. Commonly found in riverbeds or eroding out of limestone cliffs.
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