sedimentary
Chert (Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish with distinct banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (exhibits prominent conchoidal fracture); Specific gravity: 2.6 – 2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and brownish with distinct banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish with distinct banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (exhibits prominent conchoidal fracture); Specific gravity: 2.6 – 2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine environments. This specimen appears to be a nodule or fragment found in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) and to start fires (striking steel). Modernly used as a decorative stone, in construction aggregate, and occasionally in jewelry as polished stones.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most vital resources for prehistoric humans globally due to its predictable breaking pattern (conchoidal fracture) which produces razor-sharp edges.
Field identification & locations
Identify by its 'flinty' waxy look and shell-like (conchoidal) breaks. Often found as nodules within limestone or along riverbeds where the harder chert has outlasted the surrounding softer rock. It will spark when struck against carbon steel.
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