sedimentary
Chert (or Jasper)
Microcrystalline Quartz (SiO2)
Hardness of 7 on the Mohs scale, typically brown, reddish-brown, or yellow-brown color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of roughly 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically brown, reddish-brown, or yellow-brown color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of roughly 2.60 to 2.65.
Formation & geological history
Formed in marine environments through the chemical precipitation of silica from seawater or the replacement of limestone or chalk by silica-rich solutions during diagenesis.
Uses & applications
Historically used by early humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Today used occasionally in decorative lapidary work and landscaping.
Geological facts
Chert and flint are essentially the same material; the term chert is generally applied to varieties found in limestone, while flint is often reserved for dark or black varieties found in chalk.
Field identification & locations
Easily identified in the field by its hardness (scratches glass easily), waxy luster, and sharp conchoidal fracture edges. Widely found worldwide in sedimentary rock formations.
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