sedimentary
Chert (Yellow Jasper/Flint)
Silicon dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 7 (Mohs scale), Color: tan, yellow, brownish, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, yellow, brownish, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical precipitation of silica in ocean floor sediments or limestone cavities.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to its sharp edges; modern uses include industrial abrasives, road construction, and use as gemstones or landscaping material.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create fire (when struck against steel) and high-quality sharp tools because it fractures predictably like glass.
Field identification & locations
Identify in the field by its waxy texture and distinctive shell-like (conchoidal) fractures. It will easily scratch glass but cannot be scratched by a steel knife. Found globally in sedimentary rock outcrops.
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