sedimentary
Chert / Flint
SiO2 (Silicon Dioxide)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Dull to waxy; Crystal Structure: Microcrystalline (hidden); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Dull to waxy; Crystal Structure: Microcrystalline (hidden); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms in deep-sea environments. Often occurs as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires (flint); currently used in road construction, as an abrasive, and occasionally in jewelry as cabochons.
Geological facts
Because of its conchoidal fracture, chert breaks into very sharp edges, making it the primary material for prehistoric arrowheads and spear points.
Field identification & locations
Identify by its hardness (will scratch glass), smooth waxy feel on breaks, and sharp edges. Common in sedimentary basins worldwide.
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