metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White to gray, often with reddish or yellowish tints from iron impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to gray, often with reddish or yellowish tints from iron impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. It can be found in mountain belts and areas of tectonic activity across various geological eras.
Uses & applications
Used as crushed stone for road construction and railroad ballast. In high-quality forms, it is used for floor tiles, countertops, and as dimension stone in architecture. High purity quartzite is a source of silica for glassmaking.
Geological facts
Quartzite is so hard that it will scratch glass and even high-quality steel. Unlike sandstone, which breaks around its sand grains, quartzite is so well-fused that it breaks directly through the constituent grains.
Field identification & locations
Identify in the field by its extreme hardness, grainy sugary texture, and lack of reaction to acid. It is commonly found globally, particularly in the Appalachian Mountains, the Great Lakes region, and the Alps.
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