sedimentary
Chert / Jasper Pebble
Microcrystalline Quartz (SiO2)
Mohs hardness of 6.5 to 7. Color ranges from tan, brown, yellowish to dark brown/grey with sub-conchoidal fracture and a dull to waxy luster. Dense and fine-grained.
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Physical properties
Mohs hardness of 6.5 to 7. Color ranges from tan, brown, yellowish to dark brown/grey with sub-conchoidal fracture and a dull to waxy luster. Dense and fine-grained.
Formation & geological history
Formed through the accumulation and recrystallization of silica-rich fluids or biological deposits (microscopic organism shells like radiolarians) within sedimentary strata.
Uses & applications
Historically used for stone tools like arrowheads due to conchoidal fracturing. Modern usage includes gravel, lapidary polishing, and casual collecting.
Geological facts
Chert and jasper are composed of microscopic quartz crystals. They are extremely durable and frequently found as rounded river or beach pebbles after enduring extensive water erosion.
Field identification & locations
Identified by its smooth, polished texture from water weathering, high hardness (cannot be scratched by a steel blade), and waxy surface luster. Common in stream beds, gravel deposits, and beaches worldwide.
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