sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in marine environments. Prevalent in limestone and chalk deposits.
Uses & applications
Historically used for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as a refractory material.
Geological facts
Because it breaks with a conchoidal fracture, it was the primary material for arrowheads and spear points in the Stone Age. It is chemically identical to quartz but with a much finer grain.
Field identification & locations
Identify by its waxy texture and sharp, shell-like (conchoidal) edges when broken. It will scratch glass easily. Commonly found in riverbeds or as nodules within limestone layers.
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