metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: tan, brownish, or pinkish due to iron impurities, Luster: vitreous to dull, Crystal structure: hexagonal/trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brownish, or pinkish due to iron impurities, Luster: vitreous to dull, Crystal structure: hexagonal/trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under extreme heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction as crushed stone for road ballast, as dimension stone for wall coverings and flooring, and occasionally in glassmaking if pure enough.
Geological facts
Quartzite is so durable that it often forms the crests of ridges and mountain ranges. It is significantly harder than the sandstone it originates from and will scratch steel and glass easily.
Field identification & locations
Identify in the field by its extreme hardness and grainy texture that looks like sandstone but breaks across the grains rather than around them. Found globally in metamorphic terranes.
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