metamorphic
Blue Quartzite
Metamorphosed Quartz (SiO2) with inclusions
Hardness: 7 on Mohs scale; Color: Grayish-blue to deep blue; Luster: Vitreous to waxy; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.63–2.65
- Hardness
- 7 on Mohs scale
- Color
- Grayish-blue to deep blue
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-blue to deep blue; Luster: Vitreous to waxy; Crystal structure: Trigonal (granular); 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 color is often caused by inclusions of fibrous blue minerals like crocidolite, dumortierite, or tourmaline.
Uses & applications
Used as a decorative building stone, for countertops, landscaping, and as a semi-precious gemstone in jewelry and tumbled stones.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, appearing as ridges or hills. It is often confused with marble but is significantly harder and will not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of reaction to hydrochloric acid. Commonly found in old mountain ranges like the Appalachians or the Blue Ridge Mountains.
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