sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Gray, tan, white, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Gray, tan, white, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Gray, tan, white, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in groundwater within limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used as road aggregate, in glass manufacturing, and as decorative gravel.
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture creates extremely sharp edges for knives and arrowheads.
Field identification & locations
Identify in the field by its smooth, waxy surface and curved, glass-like fracture edges. It is often found as nodules or layers within sedimentary rock formations.
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Brecciated Chert (Microcrystalline Silica)
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