sedimentary
Chert (Jasper)
Chert / Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, grey, and tan banding; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Reddish-brown, grey, and tan banding
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, grey, and tan banding; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the precipitation of silica-rich fluids within sedimentary rock layers or as microfossils (radiolarians/diatoms) on the ocean floor. Most specimens found today date from various eras, frequently Paleozoic to Cenozoic.
Uses & applications
Historically used for making stone tools (flintknapping); currently used in jewelry (cabochons), as decorative landscaping stones, and for lapidary art.
Geological facts
Chert is so hard that it was once the primary material for starting fires and crafting arrowheads before the advent of metallurgy. Red varieties are specifically called Jasper when they contain iron inclusions.
Field identification & locations
Identify in the field by its smooth, waxy feel and characteristic seashell-like (conchoidal) fractures. It is commonly found in riverbeds or within limestone and dolomite formations. It will scratch glass easily.
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