sedimentary
Chert (often called Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, yellow-brown, or mustard; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, yellow-brown, or mustard
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, yellow-brown, or mustard; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic crystals); 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 chemical precipitation from groundwater within sedimentary layers like limestone or chalk.
Uses & applications
Historically used for stone tools due to its sharp edges when fractured; modernly used in road construction, as decorative gravel, or for lapidary work.
Geological facts
Chert was one of the most important minerals to prehistoric humans for crafting arrowheads and spear tips because of its predictable conchoidal fracture pattern.
Field identification & locations
Identify in the field by its hardness (it will scratch glass and steel) and its waxy surface texture. This small specimen appears to be a water-worn river pebble, found commonly in gravel pits or stream beds.
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