sedimentary
Likely chert (flint)
Microcrystalline quartz (SiO₂), commonly called chert; identification from the photo is tentative.
AI-generated identification · may be incorrectDark brown to gray, dull weathered exterior with lighter fracture surfaces; quartz-rich and typically Mohs 7, with a waxy to dull luster and no cleavage. The fine-grained texture shows no visible crystals; specific gravity is about 2.6.
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Physical properties
Dark brown to gray, dull weathered exterior with lighter fracture surfaces; quartz-rich and typically Mohs 7, with a waxy to dull luster and no cleavage. The fine-grained texture shows no visible crystals; specific gravity is about 2.6.
Formation & geological history
Forms when silica accumulates or replaces material in sedimentary settings, often as nodules in limestone or chalk. Chert occurs in rocks of many geological ages.
Uses & applications
Historically used for cutting tools and fire-starting; today collected and sometimes used decoratively or as aggregate.
Geological facts
Fresh chert fractures with curved, shell-like (conchoidal) surfaces and can produce very sharp edges.
Field identification & locations
Look for hardness, lack of cleavage, and conchoidal fracture; common worldwide in sedimentary formations. The specimen’s rough, weathered appearance fits chert, but the photo alone cannot confirm it.
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