sedimentary
Chert (specifically Red Chert or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale). Color: Reddish-brown, tan, and grey. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Reddish-brown, tan, and grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale). Color: Reddish-brown, tan, and grey. Luster: Dull 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 within sedimentary rock layers. Often found in nodules or bedded deposits within limestone or dolomite.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp edges. Modernly used in jewelry (as jasper), as road metal, and as a decorative rock for landscaping.
Geological facts
Chert was one of the first materials used by early humans for tool manufacturing because it breaks with a predictable, razor-sharp conchoidal fracture. Red varieties are often called Jasper when they are opaque and rich in iron oxides.
Field identification & locations
Identify in the field by its hardness (it can scratch glass), its smooth 'shell-like' conchoidal fracture patterns, and its dense, non-porous texture. Found globally in ancient seabed environments.
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