sedimentary
Chert (Iron-Stained)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale), Color: Cream with orange-brown iron staining, Luster: Waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Cream with orange-brown iron staining, Luster: Waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains or through the chemical precipitation of silica in marine environments. Iron staining occurs through groundwater leaching.
Uses & applications
Historically used for arrowheads and tools; currently used in decorative landscaping and as an industrial abrasive.
Geological facts
Chert is so hard it can strike sparks against steel. Often called flint when found in chalk or marl, it is one of the most durable sedimentary rocks.
Field identification & locations
Identify by its 'slick' waxy feel, conchoidal (shell-like) fracture edges, and inability to be scratched by a steel knife. Commonly found in riverbeds and limestone outcrops.
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