sedimentary
Chert on Volcanic Host Rock
Sedimentary Chert (SiO2) within Basalt or Andesite
Hardness: 6.5-7 (chert) / 5.5-6 (host); Color: white, tan, and reddish-orange (chert) on dark grey/black (lava); Luster: waxy to dull; Structure: microcrystalline silica.
- Hardness
- 6
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 (chert) / 5.5-6 (host); Color: white, tan, and reddish-orange (chert) on dark grey/black (lava); Luster: waxy to dull; Structure: microcrystalline silica.
Formation & geological history
Formed when silica-rich fluids precipitated into cavities and fractures of volcanic host rock (igneous), likely during hydrothermal cooling phases. The red color is due to iron oxide inclusions.
Uses & applications
Primarily for mineral collecting and landscape decoration. Historically, chert and flint were used for making sharp tools and arrowheads.
Geological facts
Chert is so durable that it often remains as 'float' long after the surrounding softer volcanic rock has weathered away. This specimen is a good example of secondary mineral deposition.
Field identification & locations
Identified by its conchoidal fracture and hardness (won't be scratched by a steel blade). Common in volcanic fields across the Western United States and Iceland.
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Chert Breccia
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