sedimentary
Chert (Nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, reddish; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, reddish
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, reddish; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through a chemical process where silica-rich fluids replace organic material or fill voids in limestone or chalk beds. Often Paleozoic to Mesozoic in age. Found in marine sedimentary environments.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used in construction aggregate, as road surfacing, and occasionally for lapidary work (polishing/tumbling).
Geological facts
Because it breaks with a conchoidal fracture (smooth, curved surfaces), it was the primary material used by prehistoric humans to create sharp cutting tools and weapons.
Field identification & locations
Identify by its 'waxy' appearance and smooth, glass-like fracture surfaces when chipped. Commonly found in gravel beds or eroding out of limestone outcrops worldwide. Collectors look for unique banding or color patterns.
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