sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, brown with reddish iron staining, Luster: waxy to dull, Crystal Structure: trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, brown with reddish iron staining, Luster: waxy to dull, Crystal Structure: trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools and fire-starting. Currently used in road construction, as an abrasive, and by hobbyists for flintknapping.
Geological facts
Chert was one of the most important raw materials for early humans because its conchoidal fracture creates edges sharper than a steel scalpel.
Field identification & locations
Identified by its extreme hardness (scratches glass), waxy texture on fresh breaks, and smooth, curved (shell-like) fracture surfaces. Commonly found in riverbeds and limestone outcrops.
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Brown Sandstone (River Rock)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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