sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Grey, brown, yellowish, or black; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Conchoidal fracture; Specific gravity: 2.65.
- Hardness
- 6
- Color
- Grey, brown, yellowish, or black
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Grey, brown, yellowish, or black; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Conchoidal fracture; Specific gravity: 2.65.
Formation & geological history
Formed in marine or freshwater environments as a result of the accumulation of siliceous remains (like diatoms or radiolarians) or via chemical precipitation in limestone/dolomite cavities.
Uses & applications
Used historically for stone tools and weapons; currently used in construction as road aggregate, decorative landscaping, and occasionally as a gemstone (Jasper varieties).
Geological facts
Chert has a conchoidal fracture pattern that creates razor-sharp edges, which is why it was the primary material for prehistoric arrowheads, scrapers, and knives.
Field identification & locations
Identify by its waxy luster, extreme hardness (scratches glass), and smooth, shell-like fracture surfaces. Often found as nodules within limestone or as bedded deposits.
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