sedimentary
Chert (Pebble)
Microcrystalline Quartz (SiO2)
Hardness of 7 on Mohs scale; dull to waxy luster; microcrystalline/cryptocrystalline structure; conchoidal fracture with sharp edges; earthy brownish-gray color.
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Physical properties
Hardness of 7 on Mohs scale; dull to waxy luster; microcrystalline/cryptocrystalline structure; conchoidal fracture with sharp edges; earthy brownish-gray color.
Formation & geological history
Formed through the accumulation and precipitation of silica-rich biogenic sediments (such as radiolaria or diatoms) or chemical precipitation in sedimentary basins.
Uses & applications
Historically used by ancient humans for stone tools, flintknapping, and fire-starting. Today used primarily as construction aggregate or road gravel.
Geological facts
Chert is extremely durable and weather-resistant, which allows it to survive long distances of river transport, forming rounded river pebbles like this sample.
Field identification & locations
Can be identified by its hardness (scratches glass), smooth conchoidal fracture, and lack of visible grains. Abundant worldwide in riverbeds, gravel pits, and limestone formations.
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