sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: tan, brown, reddish-orange; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- tan, brown, reddish-orange
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: tan, brown, reddish-orange; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments, often replacing original limestone or chalk during diagenesis.
Uses & applications
Historically used for making stone tools (arrowheads); currently used in road construction, as an abrasive, and occasionally for lapidary work if highly colored.
Geological facts
Chert is so hard it can scratch steel. It is one of the most common materials used by prehistoric humans for tool-making because it breaks with sharp edges like glass.
Field identification & locations
Identify by its 'flint-like' waxy texture, smooth conchoidal (shell-like) fracture surfaces, and high hardness. Commonly found in riverbeds, glacial tills, and as nodules in limestone outcrops.
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