sedimentary
Chert (Iron-stained)
Chert (SiO2)
Hardness: 7 (Mohs), Color: Tan, brown, and grey with iron staining, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Tan, brown, and grey with iron staining, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater within sedimentary beds. This specimen shows significant weathering and secondary iron oxidation.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modernly used as road aggregate or in landscaping.
Geological facts
Chert is so hard it can scratch glass and steel. It is chemically identical to quartz but has a different internal structure. Because of its durability, it often survives long after the surrounding rock has weathered away.
Field identification & locations
Identify in the field by its hardness and the way it breaks into sharp, curved flakes (conchoidal fracture). It is ubiquitous in limestone and chalk formations worldwide.
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