sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Sage green to tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Cleavage: None
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Physical properties
Hardness: 7 (Mohs scale), Color: Sage green to tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Cleavage: None
Formation & geological history
Formed by the accumulation and subsequent replacement of silica-rich materials in marine environments, often from the remains of diatoms or radiolarians. This specimen shows typical chemical weathering on its exterior.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include road surfacing, jewelry (green varieties as jasper), and as fire-starting flints.
Geological facts
Chert is essentially the same as flint, though the name 'flint' is often reserved for specimens found in chalk or marl. It can preserve tiny micro-fossils that are millions of years old.
Field identification & locations
Identified in the field by its extreme hardness (scratches glass), waxy texture, and smooth, curved conchoidal fracture patterns when broken. Commonly found in limestone or dolomite beds.
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