sedimentary
Chert (Flint/Jasper variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white to tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white to tan; 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 radiolarians or diatoms) or chemical precipitation from groundwater within limestone or chalk beds. Can range from Precambrian to Holocene in age.
Uses & applications
Historically used for stone tools/weapons due to sharp edges; currently used for road surfacing, as an abrasive, and in some jewelry (as jasper or agate varieties).
Geological facts
Chert was one of the first materials used by prehistoric humans to create 'fire-starters' and sharp arrowheads because it breaks into very sharp, predictable flakes.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its curved, glass-like 'conchoidal' fracture patterns. Often found as nodules in limestone outcrops.
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