sedimentary
Chert (often called Jasper or Flint in this color variety)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Variegated red, grey, green, and brown; Luster: Vitreous to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Variegated red, grey, green, and brown
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Variegated red, grey, green, and brown; Luster: Vitreous to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the recrystallization of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in sedimentary layers or volcanic cavities.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used as decorative stones, gemstones (as Jasper), and in some industrial grinding applications.
Geological facts
Because of its conchoidal fracture (breaking like glass with sharp edges), it was the primary material for prehistoric toolmaking globally for thousands of years.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy luster, and curved 'scalloped' fracture edges. Commonly found in limestone beds or as nodules in volcanic soil.
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