sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: dull gray to greenish-gray, Luster: waxy to vitreous, Structure: microcrystalline, Cleavage: none (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: dull gray to greenish-gray, Luster: waxy to vitreous, Structure: microcrystalline, Cleavage: none (conchoidal fracture)
Formation & geological history
Formed primarily as chemical precipitates from silica-rich fluids in marine environments or by the replacement of carbonate minerals in sedimentary sequences.
Uses & applications
Historically used for stone tools and weapons (flintknapping). Currently used as road aggregate and as an ornamental garden stone.
Geological facts
Chert is so hard that it can strike sparks against steel. It is one of the most common materials used by early humans for making arrowheads and spear points.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in limestone beds and river deposits.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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