sedimentary
Chert (specifically Yellow/Common Opal or Jasper mixture)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Opaque yellow to tan with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Opaque yellow to tan with waxy luster
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Opaque yellow to tan with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils on ancient seafloors or by inorganic precipitation from silica-saturated fluids in limestone or volcanic cavities.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include lapidary work, decorative landscaping, and as a raw material for silicon-based products.
Geological facts
Chert is remarkably durable and resistant to weathering. It was one of the first materials used by early humans to create sparking tools for fire and sharp edges for survival.
Field identification & locations
Identify in the field by its smooth, waxy surface and its tendency to break into sharp, curved edges like glass. Often found in stream beds or within limestone outcrops.
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