sedimentary
Chert (likely flint)
Microcrystalline quartz, SiO₂
AI-generated identification · may be incorrectHardness 6.5–7; cream to tan with a brown-gray weathered cortex. Waxy to dull luster, cryptocrystalline structure, and no visible cleavage; breaks with a curved, sharp conchoidal fracture.
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Physical properties
Hardness 6.5–7; cream to tan with a brown-gray weathered cortex. Waxy to dull luster, cryptocrystalline structure, and no visible cleavage; breaks with a curved, sharp conchoidal fracture.
Formation & geological history
Forms when silica accumulates and recrystallizes in sedimentary rocks, often replacing limestone or filling cavities. The image alone cannot determine its geological age.
Uses & applications
Chert has been used for tools and fire-starting; attractive pieces are collected, and some varieties are cut for decorative objects.
Geological facts
Its exceptionally sharp fracture edges made it an important prehistoric tool material.
Field identification & locations
Look for hardness, waxy appearance, and conchoidal fracture; cream interiors with darker cortex are common in flint nodules. Chert occurs worldwide in sedimentary formations, especially limestone and chalk.
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