metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale), Color: Blue-grey/Grey, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: Indistinct/Conchoidal fracture, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Blue-grey/Grey, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: Indistinct/Conchoidal fracture, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together into a dense, interlocking network of crystals.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists weathering better than the surrounding rock types.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks through quartz grains rather than around them. Common in folded mountain belts and ancient shield areas.
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