sedimentary
Chert (likely flint)
Microcrystalline quartz (SiO₂), varieties commonly called chert or flint
AI-generated identification · may be incorrectHardness about 7 Mohs; reddish-brown with a waxy to dull luster and a gray-brown, shell-like conchoidal fracture. Composed mainly of microcrystalline quartz; no visible cleavage or crystals.
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Physical properties
Hardness about 7 Mohs; reddish-brown with a waxy to dull luster and a gray-brown, shell-like conchoidal fracture. Composed mainly of microcrystalline quartz; no visible cleavage or crystals.
Formation & geological history
Forms when silica accumulates and hardens in sedimentary settings, often replacing carbonate material. Its exact age and geological source cannot be determined from the photo.
Uses & applications
Historically used for stone tools and fire-starting; today collected and sometimes used decoratively.
Geological facts
The sharp edges and curved fracture surfaces are characteristic of knappable chert.
Field identification & locations
Look for hardness, a smooth conchoidal fracture, and edges that can be very sharp; chert occurs widely in sedimentary rocks. A small common fragment is typically worth about $1–$10; worked or notable specimens may sell for more.
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