sedimentary
Chert (Jasper)
Microcrystalline Silica (SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Opaque reddish-brown and tan earthy tones. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Opaque reddish-brown and tan earthy tones
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Opaque reddish-brown and tan earthy tones. 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 (radiolarites or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in Precambrian to Cenozoic formations.
Uses & applications
Historically used for stone tools (flintknapping); modern uses include lapidary art, jewelry (as jasper), and as decorative landscaping stones.
Geological facts
Reddish chert is often called Jasper due to iron oxide impurities. It was one of the most important minerals for early humans because its conchoidal fracture creates razor-sharp edges.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth shell-like fracture surface, and lack of visible grains. Found globally in limestone formations or as river cobbles.
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