sedimentary
Chert (often called Flint)
Microcrystalline quartz (SiO2)
Hardness: 7 (Mohs); Color: Dark gray, black, or brown with light bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture)
- Hardness
- 7 (Mohs)
- Color
- Dark gray, black, or brown with light bands
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 (Mohs); Color: Dark gray, black, or brown with light bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture)
Formation & geological history
Formed in sedimentary environments from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or through chemical precipitation in limestone/chalk beds.
Uses & applications
Historically used for stone tools and starting fires (flintknapping); currently used in road construction, jewelry (as jasper/agate varieties), and as a decorative stone.
Geological facts
Flint was one of the first materials used by early humans for sophisticated tool-making due to its predictable conchoidal fracturing which creates razor-sharp edges.
Field identification & locations
Identify in the field by its smooth, glass-like fracture surfaces and ability to scratch steel and glass. Commonly found as nodules in chalk or limestone deposits globally.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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