sedimentary
Chert (often called Flint or Jasper)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, cream, and grey with iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, tan, cream, and grey with iron staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, cream, and grey with iron staining; Luster: Waxy to dull; 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. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (knapping); currently used as an abrasive, in construction aggregate, and as a decorative landscape stone.
Geological facts
Chert has a conchoidal fracture which creates sharp edges, making it the primary material for prehistoric arrowheads and spear points. Different colors are often caused by trace impurities like iron oxide.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy texture, and the way it breaks into curved, shell-like flakes. Found globally in sedimentary basins.
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