sedimentary
Chert
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Commonly Paleozoic to Mesozoic in age.
Uses & applications
Historically used for stone tools and weapons; currently used as road aggregate, in construction, and occasionally as a gemstone (Jasper varieties).
Geological facts
Chert is essentially the same as flint, though 'flint' is often specifically used for chert found in chalk. It was one of the first materials humans traded over long distances in the Stone Age.
Field identification & locations
Identify by its waxy luster, extreme hardness (scratches glass), and shell-like curves (conchoidal fracture) when broken. Often found in nodules within limestone outcrops.
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