sedimentary
Chert (varietal Chalcedony or Flint)
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: Brownish-tan with waxy patches, Luster: Waxy to dull, Crystal structure: Cryptocrystalline (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-tan with waxy patches, Luster: Waxy to dull, Crystal structure: Cryptocrystalline (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 the replacement of limestone by silica-rich groundwater. Often found in nodules within sedimentary rock layers from various geological ages.
Uses & applications
Historically used for stone tools and fire-starting (flint). Currently used in road construction, as a landscaping material, and in jewelry (when decorative varieties like jasper or agate are present).
Geological facts
Chert has a unique 'conchoidal' fracture, meaning it breaks like glass to produce sharp edges. This made it the primary material for arrowheads and spear tips for thousands of years of human history.
Field identification & locations
Identify in the field by its hardness (it can scratch glass and steel), its waxy feel, and the distinctive curved, shell-like (conchoidal) breaks on its surface. Commonly found in riverbeds or eroded limestone deposits.
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