metamorphic
Blue Quartzite
Quartzite (primarily SiO2 with inclusions like Dumortierite or Magnesio-riebeckite)
Hardness: 7 (Mohs scale); Color: Pale to deep blue with white/gray banding; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal) microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.63–2.65
- Hardness
- 7 (Mohs scale)
- Color
- Pale to deep blue with white/gray banding
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Pale to deep blue with white/gray banding; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal) microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.63–2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. The blue coloration is typically caused by micro-inclusions of blue minerals like dumortierite.
Uses & applications
Used primarily in decorative construction (countertops, tiles), as a gemstone for lapidary work (cabochons, beads), and as a landscaping stone. It is also a popular collector's specimen due to its unique color.
Geological facts
Unlike 'Blue Quartz' (which is often macrocrystalline quartz with inclusions), Blue Quartzite is a solid metamorphic rock where the individual sand grains have been entirely recrystallized. It is exceptionally durable and resistant to chemical weathering.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture under a hand lens. It lacks the salty taste of halite or the softness of calcite. Common locations include Brazil, South Africa, and the Blue Ridge Mountains in the USA.
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