metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to buff/yellowish, Luster: vitreous to dull, Crystal structure: granular/interlocking, Cleavage: none (breaks across grains), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to buff/yellowish, Luster: vitreous to dull, Crystal structure: granular/interlocking, Cleavage: none (breaks across grains), Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone under high heat and pressure, causing the original quartz grains to recrystallize into a dense, crystalline mass.
Uses & applications
Used in road construction, as railroad ballast, for heavy-duty floor tiles, and as a raw material for glass making and metallurgy. High-quality specimens are used for decorative landscaping.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of hills and ridges. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, granular texture. Unlike sandstone, when broken, quartzite fractures through the quartz grains rather than around them.
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