sedimentary
Chert (varieties include Flint and Jasper)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: ranges from grey, black, and brown to reddish (jasper); Luster: vitreous to waxy; Structure: microcrystalline quartz; Fracture: conchoidal (shell-like); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- ranges from grey, black, and brown to reddish (jasper)
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: ranges from grey, black, and brown to reddish (jasper); Luster: vitreous to waxy; Structure: microcrystalline quartz; Fracture: conchoidal (shell-like); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or chemical precipitation from groundwater within limestone or chalk beds. Age can range from Precambrian to Holocene.
Uses & applications
Used historically for stone tools and starting fires (flint); modern uses include construction aggregate, gemstones (jasper), and as a component in glassmaking and abrasives.
Geological facts
Chert was foundational to the Stone Age; its ability to break into razor-sharp edges made it the primary material for arrowheads, scrapers, and knives for thousands of years.
Field identification & locations
Identify by its 'conchoidal' fracture—the way it breaks into smooth, curved surfaces with sharp edges. It is found globally, often as nodules in limestone or as solid bedded deposits in marine sedimentary rocks.
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