sedimentary
Chert Fossil (Pebble)
Microcrystalline Quartz (SiO2) with biogenic inclusions
Hardness: 7 (Mohs scale), Color: tan to grayish-green with white patterning, Luster: waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to grayish-green with white patterning, Luster: waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed via the chemical precipitation of silica-rich fluids in marine sedimentary environments where organic matter or shell fragments serve as a nucleus. Often found as water-worn pebbles in riverbeds or coastal areas.
Uses & applications
Used historically for stone tools due to its sharp edges; currently used for landscaping, as a lapidary material for polishing, and as a geological teaching specimen.
Geological facts
The circular and curved white patterns on the surface are likely partially silicified fossil fragments such as crinoid stems, bryozoans, or small shell bits that have been eroded and smoothed by water action.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife), waxy feel, and smooth, rounded water-worn shape. Commonly found in gravel pits and beaches near sedimentary basins.
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