sedimentary
Chert (Nodule)
Chert (variety of microcrystalline quartz, SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: Dark brown, black, and reddish-brown, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark brown, black, and reddish-brown, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of silica-rich marine organisms. Often found as nodules within limestone or chalk beds. Period range varies from Precambrian to current.
Uses & applications
Historically used for making stone tools (flintknapping); currently used as an abrasive, decorative stone in landscaping, or as a gemstone if colorful (Jasper).
Geological facts
Chert is so hard it can scratch steel. It was one of the most important materials for early humans because its conchoidal fracture produces extremely sharp edges, ideal for arrowheads and spears.
Field identification & locations
Identify by its extreme hardness, waxy appearance, and smooth, curved shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or within sedimentary rock formations.
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