metamorphic
Quartzite
Quartzite (chiefly SiO2)
Hardness: 7 (Mohs scale), Color: tan-gray, Luster: dull to vitreous, Structure: granular interlocking crystals, Cleavage: none, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan-gray, Luster: dull to vitreous, Structure: granular interlocking crystals, Cleavage: none, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone under heat and pressure. The original quartz sand grains recrystallize into a dense, interlocking mosaic of quartz crystals.
Uses & applications
Primarily used in construction for road ballast, roofing granules, and as a dimension stone. It is also used as a source of silica for glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the capstone of hills and mountain ridges because it resists weathering better than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (will scratch glass and steel) and its sandy texture that does not rub off easily. Commonly found in folded mountain belts globally.
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