sedimentary
Chert (specifically varieties like Chalcedony or Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Waxy white, grey, beige with slight translucency; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Waxy white, grey, beige with slight translucency
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Waxy white, grey, beige with slight translucency; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Common in limestone or chalk beds, often dating from the Paleozoic to Mesozoic eras.
Uses & applications
Used historically for stone tools (knapping), flintlock firearms, and modern decorative stones. High-quality colorful specimens are used in jewelry as cabochons.
Geological facts
Chert breaks with a conchoidal fracture, creating sharp edges that were essential for arrowhead and scraper manufacturing by prehistoric humans.
Field identification & locations
Identify by its waxy appearance, extreme hardness (scratches glass), and the curved or scalloped way it breaks. Look for it in river beds or errodable limestone outcrops.
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