sedimentary
Chert (Red Jasper variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown with white inclusions; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Reddish-brown with white inclusions
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown with white inclusions; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in sedimentary basins. The red color is caused by iron oxide (hematite) impurities.
Uses & applications
Historically used for stone tools and arrowheads; currently used in lapidary work, jewelry, and as decorative stone in landscaping.
Geological facts
Chert is so hard it can strike sparks from steel, leading to its widespread use as gunflints in early firearms.
Field identification & locations
Identify by its 'glassy' conchoidal fracture patterns and inability to be scratched by a steel knife. Often found in riverbeds or as nodules within limestone or chalk formations.
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