sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan to light brown with white crust, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to light brown with white crust, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed in marine environments through the accumulation of siliceous remains of organisms like diatoms or radiolaria, or by chemical precipitation from silica-rich fluids within limestone or chalk beds.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a polishing media in rock tumblers.
Geological facts
This specimen appears to be a small fragment of chert or flint. Because of its high hardness and conchoidal fracture, it can be struck against steel to create sparks, a method used for centuries to start fires.
Field identification & locations
Identified by its waxy texture, extreme hardness (scratches glass), and sharp, shell-like fracture edges. Commonly found as nodules or layers within sedimentary rock formations.
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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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