sedimentary
Chert (often called Jasper or Flint)
Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Brown, tan, and cream mottling; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 7 Mohs
- Color
- Brown, tan, and cream mottling
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Brown, tan, and cream mottling; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or through chemical precipitation from silica-rich fluids within other sedimentary rocks like limestone. Often found in nodes or beds.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges; currently used for lapidary work, jewelry, and landscaping.
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture allows it to be shaped into extremely sharp tools.
Field identification & locations
Identify by its hardness (scratches glass), waxy texture when broken, and smooth shell-like (conchoidal) fractures. Common in riverbeds and limestone outcrops.
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