sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Tan, brown, grey, or black. Luster: Waxy to dull. Crystal Structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6 – 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Tan, brown, grey, or black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Tan, brown, grey, or black. Luster: Waxy to dull. Crystal Structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6 – 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the replacement of carbonate minerals in limestone or chalk beds. Often found in nodules or bedded deposits and can range from Precambrian to recent geological ages.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in road construction, as an abrasive, and sometimes in jewelry as tumbled stones.
Geological facts
Flint is a variety of chert that was the first 'high-tech' material of human history, used to start fires and create weaponry. It sparks when struck against steel due to its hardness and silica content.
Field identification & locations
Identify in the field by its characteristic conchoidal (shell-like) fracture patterns and ability to scratch glass. It is commonly found in limestone outcrops, riverbeds, and gravel pits. Collectors look for smooth, waxy surfaces and interesting color patterns.
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