sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Gray, black, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Gray, black, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Gray, black, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments like deep-sea floors. It often occurs as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (knapping); currently used as abrasive media, in road construction, and as fire-starting flints.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. It produces sparks when struck against steel due to its hardness and chemical composition.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture pattern and its ability to scratch glass. Commonly found in stream beds and areas with limestone outcrops.
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