sedimentary
Chert (likely flint)
Microcrystalline quartz, SiO₂ (chalcedony/quartz)
AI-generated identification · may be incorrectGray-brown, opaque, with a dull to slightly waxy luster and conchoidal fracture producing sharp edges; Mohs hardness about 7, no cleavage, cryptocrystalline structure, and specific gravity near 2.6.
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Physical properties
Gray-brown, opaque, with a dull to slightly waxy luster and conchoidal fracture producing sharp edges; Mohs hardness about 7, no cleavage, cryptocrystalline structure, and specific gravity near 2.6.
Formation & geological history
Forms when silica-rich groundwater replaces or fills pores in limestone, commonly as nodules or beds. It can form during many geological periods; age cannot be determined from the image.
Uses & applications
Used historically for stone tools and fire-starting; attractive pieces may be collected, but this small rough specimen has little commercial value.
Geological facts
The fracture surfaces and angular flake scars are characteristic of chert and can resemble deliberate knapping, though natural breakage is also possible.
Field identification & locations
Identify it by testing whether it scratches glass, observing its glassy conchoidal fracture, and checking for absence of visible grains or cleavage. Common in limestone regions worldwide, including chalk and marine sedimentary formations.
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