sedimentary
Chert or flint fragment
Microcrystalline quartz (SiO₂), commonly called chert; dark varieties are flint
AI-generated identification · may be incorrectTypically hardness 6.5–7, waxy to dull luster, conchoidal fracture, and gray-brown to black color; the pictured small, dark, smooth-edged fragment is consistent with this material, though image identification is limited.
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Physical properties
Typically hardness 6.5–7, waxy to dull luster, conchoidal fracture, and gray-brown to black color; the pictured small, dark, smooth-edged fragment is consistent with this material, though image identification is limited.
Formation & geological history
Forms when silica-rich groundwater replaces or precipitates within marine limestone, commonly during the Paleozoic–Cenozoic; flint is especially associated with chalk deposits.
Uses & applications
Used historically for sharp tools and fire-starting; today it is mainly a teaching, archaeological, lapidary, or decorative specimen, with little industrial value as a small fragment.
Geological facts
Freshly broken chert produces very sharp edges and may strike sparks from steel; red or brown coloration commonly reflects iron oxides.
Field identification & locations
Look for conchoidal fracture, glassy or waxy surfaces, absence of visible grains, and a scratch resistance near quartz; common in limestone, chalk, gravel, and glacial deposits worldwide.
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