metamorphic
River Quartzite or Chert Pebble
Quartzite (primarily Silicon Dioxide - SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-tan rind with a grayish-green interior; Luster: Dull to waxy; Texture: Fine-grained, microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-tan rind with a grayish-green interior
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-tan rind with a grayish-green interior; Luster: Dull to waxy; Texture: Fine-grained, microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure Recrystallize the sand grains into a dense rock. The yellow/orange exterior is a 'weathering rind' caused by iron oxidation from long-term exposure to water and air.
Uses & applications
Common river stones are used for landscaping, construction aggregate, and ballast. High-purity quartzite is also used to produce silicon for glass and electronics.
Geological facts
Quartzite is so durable that it can outlast the mountains it originated from, surviving millions of years of water erosion in riverbeds. The yellow coating is actually a form of natural rust (Goethite or Limonite) staining the outer layers.
Field identification & locations
Identify by its ability to scratch glass and lack of reaction to acid. Often found in riverbeds, glacial deposits, and mountain foot-slopes. Collectors look for unique banding or internal translucency.
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