metamorphic
Blue Quartzite (River Pebble)
Quartzite (primarily SiO2 with Dumortierite or Crocidolite inclusions)
Hardness: 7 on Mohs scale; Color: Grayish-blue to denim blue; Luster: Dull to waxy when unpolished; Structure: Non-foliated, granular; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Grayish-blue to denim blue
- Luster
- Dull to waxy when unpolished
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-blue to denim blue; Luster: Dull to waxy when unpolished; Structure: Non-foliated, granular; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse. The blue tint is often due to the inclusion of minerals like dumortierite. This specimen exhibits a rounded shape due to fluvial (river) or glacial erosion over thousands of years.
Uses & applications
Used as decorative stone in landscaping, aquarium gravel, or polished into 'worry stones' and cabochons for jewelry. Industrially, crushed quartzite is used in road construction and as a source of silica.
Geological facts
Quartzite is so hard that it will scratch glass and steel. Unlike sandstone, which breaks around its sand grains, quartzite breaks across the grains because the crystalline bond is so strong.
Field identification & locations
Identify in the field by its hardness (it cannot be scratched by a knife) and its grainy, 'sugary' texture. Commonly found in areas with ancient mountain belts or in riverbeds downstream from metamorphic outcrops.
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