sedimentary
Chert (often called Flint or Jasper based on color)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Highly variable, commonly brown, gray, or white with waxy luster. Crystal structure: Trigonal (microscopic). Cleavage: None (exhibits conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
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Physical properties
Hardness: 7 on Mohs scale. Color: Highly variable, commonly brown, gray, or white with waxy luster. Crystal structure: Trigonal (microscopic). Cleavage: None (exhibits conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or inorganic precipitation from silica-rich fluids. It occurs as nodules or layered beds within carbonate rocks like limestone or dolomite.
Uses & applications
Historically used for stone tools and weapons (arrowheads) and for starting fires. Modern use includes road surfacing, construction aggregate, and as a semi-precious gemstone when colorful (Jasper).
Geological facts
Because of its conchoidal fracture, it breaks with sharp edges, making it the primary material for prehistoric 'stone age' technology. It is extremely resistant to chemical weathering.
Field identification & locations
Identify by its waxy luster, hardness (will scratch glass), and its characteristic shell-like (conchoidal) breakage patterns. Often found as rounded nodules in riverbeds or within limestone outcrops.
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