sedimentary
Chert (often called Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and gray; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and gray; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the precipitation of silica in groundwater within limestone or chalk beds. It can range from Precambrian to Cenozoic in age.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in construction aggregate, road surfacing, and as a semi-precious gemstone when colorful.
Geological facts
Because chert fractures in a conchoidal (shell-like) pattern with very sharp edges, it was the primary material for human survival for millions of years during the Stone Age. It produces sparks when struck against steel, leading to its use in flintlock firearms.
Field identification & locations
Identify by its waxy luster, hardness (it will scratch glass), and its characteristic smooth, curved fracture surfaces. Commonly found in stream beds or as nodules weathering out of limestone formations.
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