sedimentary
Chert (Jasper / Iron-stained Chert)
Microcrystalline Quartz (SiO2 with Fe-oxides)
Hardness 7 on the Mohs scale, waxy to dull luster, conchoidal fracture, fine-grained microcrystalline texture, yellowish-brown to tan color due to iron oxide staining.
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Physical properties
Hardness 7 on the Mohs scale, waxy to dull luster, conchoidal fracture, fine-grained microcrystalline texture, yellowish-brown to tan color due to iron oxide staining.
Formation & geological history
Formed in marine or freshwater sedimentary environments by precipitation of silica from groundwater or accumulation of biogenic siliceous oozes, followed by compaction and silicification.
Uses & applications
Historically used for flintknapping to produce arrowheads, scrapers, and blade tools. Modern uses include decorative landscaping, aggregates, and lapidary work.
Geological facts
Chert with heavy iron oxidation is often referred to as jasper or ironstone chert. Because of its extreme hardness and smooth conchoidal fracture, it was one of the primary materials used by ancient humans to craft cutting tools.
Field identification & locations
Identified in the field by its hardness (scratches glass easily), inability to be scratched by a steel nail, dull to waxy luster, sharp edges on broken surfaces, and widespread distribution in limestone beds or gravel deposits.
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