sedimentary
Chert (Commonly called Jasper or Flint)
Chert (SiO2)
Hardness: 7.0 (Mohs scale), Color: Brown, tan, and earthy tones with waxy luster. Crystal structure: Microcrystalline (Cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7
- Color
- Brown, tan, and earthy tones with waxy luster
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Physical properties
Hardness: 7.0 (Mohs scale), Color: Brown, tan, and earthy tones with waxy luster. Crystal structure: Microcrystalline (Cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation from groundwater within sedimentary layers like limestone or chalk. Many deposits date back to the Paleozoic or Mesozoic eras.
Uses & applications
Used historically for stone tools and weapons due to its sharp edges. Modern uses include road surfacing, decorative garden stones, and occasionally lapidary work for jewelry if colorful enough.
Geological facts
Because it breaks with a conchoidal fracture like glass, it was the primary material used by prehistoric humans for arrowheads and scrapers. It can spark when struck against steel.
Field identification & locations
Identify by extreme hardness (scratches glass), waxy to dull luster, and absence of visible crystals. Found globally in riverbeds, glacial tills, and sedimentary rock outcrops.
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