sedimentary
Chert (Jasper / Petrified Wood)
Microcrystalline Quartz (SiO2)
Mohs hardness of 7, reddish-brown to greyish color, waxy to vitreous luster, sharp conchoidal fracture, non-porous and fine-grained microcrystalline structure, specific gravity around 2.65.
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Physical properties
Mohs hardness of 7, reddish-brown to greyish color, waxy to vitreous luster, sharp conchoidal fracture, non-porous and fine-grained microcrystalline structure, specific gravity around 2.65.
Formation & geological history
Formed via sedimentary or secondary replacement processes where silica-rich fluids precipitated in marine environments, limestone beds, or replaced organic plant tissue (petrified wood/jasperization). Often dates from Paleozoic to Cenozoic eras.
Uses & applications
Historically used for flintknapping (stone tools, arrowheads). Modern uses include lapidary arts, decorative rock landscaping, cabochons, and gemstone collecting.
Geological facts
Chert and jasper have been utilized by humans for hundreds of thousands of years due to their ability to break with razor-sharp conchoidal edges suitable for spear points and knapping tools.
Field identification & locations
Identified by smooth, shell-like (conchoidal) fractures, high hardness (scratches steel and glass easily), and waxy luster. Commonly found in stream beds, eroded limestone formations, and volcanic ash deposits across North America and worldwide.
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