sedimentary
Chert (Flint nodules in limestone)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs); Color: tan, brown, or gray; Luster: waxy to vitreous; Crystal structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves); Specific gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- tan, brown, or gray
- Luster
- waxy to vitreous
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Physical properties
Hardness: 7 (Mohs); Color: tan, brown, or gray; Luster: waxy to vitreous; Crystal structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves); Specific gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or chemical precipitation of silica within limestone or chalk beds, often during the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as jewelry (when patterned or colorful), and as a sparking element in survival tools.
Geological facts
Flint is a variety of chert. When it breaks, it creates edges that are sharper than a surgeon's steel scalpel. It has been a primary material for human technology for over 2 million years.
Field identification & locations
Identify in the field by its smooth, waxy surface contrasting against a rougher chalk/limestone matrix. Look for curved, glass-like fracture surfaces. Often found in riverbeds or coastal chalk cliffs.
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