sedimentary
Chert (Flint/Jasper)
Silicon dioxide (SiO2) - Microcrystalline quartz
Hardness: 6.5-7 Mohs; Color: Brown to grayish-black; Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Brown to grayish-black
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown to grayish-black; Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules or layers in sedimentary rocks (like limestone) through the accumulation of silica-rich organic remains or chemical precipitation from groundwater. Age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and fire-starting (flint). Used today in ceramics, road construction, and as aquarium or landscaping gravel.
Geological facts
Because it breaks with a conchoidal fracture, it creates sharp edges that are harder than steel. It was the primary material for the 'Stone Age' technological revolution.
Field identification & locations
Identify by its waxy appearance, extreme hardness (can scratch glass), and the way it flakes into shell-like curved surfaces. Often found in chalk or limestone deposits.
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