sedimentary
Chert (often called Flint or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, yellowish-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, yellowish-brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, yellowish-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; 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. Common in limestone and chalk beds, ranging from Precambrian to Cenozoic ages.
Uses & applications
Historically used for stone tools (arrowheads). Today used in road construction, landscape gravel, and occasionally for flint-striking to produce sparks.
Geological facts
Chert breaks with a conchoidal fracture, creating sharp edges which made it the primary material for prehistoric survival tools and weapons. Yellow-brown varieties are often colored by limonite or iron oxides.
Field identification & locations
Identify by its hardness (it will scratch glass), its smooth waxy feel, and its curved, shell-like fracture pattern. Frequently found in stream beds or eroding out of limestone outcrops.
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