sedimentary
Chert (often referred to as Flint or Jasper when pigmented)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically gray, white, or reddish (due to iron oxides); Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically gray, white, or reddish (due to iron oxides)
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically gray, white, or reddish (due to iron oxides); 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 marine organisms (like diatomes or radiolarians) or by chemical precipitation from silica-rich fluids in limestone or chalk beds. Geological age ranges from Precambrian to Holocene.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, grinding media, and occasionally as a gemstone in jewelry (Jasper varieties).
Geological facts
Chert was a primary material for prehistoric humans to create arrowheads and scrapers. Flint is a specific variety of chert often found in chalk or marly limestone deposits.
Field identification & locations
Identify in the field by its distinct conchoidal (shell-like) fracture, extreme hardness (it will scratch glass), and waxy appearance. Commonly found in limestone outcrops, riverbeds, and coastal areas.
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