sedimentary
Likely weathered chert or flint
Microcrystalline quartz (SiO₂), probably chalcedony/chert
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; opaque gray-brown to tan, dull-to-waxy luster, very fine-grained with no visible crystals or cleavage. The irregular, possibly chipped surface may produce conchoidal fracture.
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Physical properties
Hardness about 6.5–7 Mohs; opaque gray-brown to tan, dull-to-waxy luster, very fine-grained with no visible crystals or cleavage. The irregular, possibly chipped surface may produce conchoidal fracture.
Formation & geological history
Forms when silica-rich groundwater replaces or cements sediment, commonly in limestone or chalk; age depends on its host formation, ranging from Paleozoic to Cenozoic. Surface brown coloration likely reflects iron-oxide weathering.
Uses & applications
Used historically for stone tools and fire-starting; today it is mainly a teaching or collecting specimen, with limited decorative use.
Geological facts
Flint is a dark variety of chert, and freshly broken surfaces can be glassy and sharp. The photograph is somewhat blurred, so exact identification is provisional.
Field identification & locations
Look for uniform microtexture, waxy luster, conchoidal chips, and inability to scratch it with a steel knife; it should scratch ordinary glass. Common in limestone and chalk regions worldwide.
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