metamorphic
Blue Quartzite
Quartzite with Dumortierite or Magnesio-riebeckite inclusions (SiO2)
Hardness: 7 (Mohs scale), Color: Sky blue to grayish-blue with rust-colored iron staining, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Sky blue to grayish-blue with rust-colored iron staining, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse, with blue coloration often resulting from mineral inclusions or Rayleigh scattering within the crystal lattice.
Uses & applications
Used as decorative stone, countertops, flooring, and in lapidary work for making cabochons or carvings. Historically used for making tools and as a source of silica.
Geological facts
Quartzite is so tough and abrasion-resistant that it often forms the crests of mountain ranges. Blue varieties are much rarer than white or pink quartzite and are highly prized by rockhounds.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its granular, sugary texture. It will break across the sand grains rather than around them. Found frequently in metamorphic belts like the Appalachians or the Canadian Shield.
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