metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, or yellowish, Luster: Vitreous to dull, Structure: Granoblastic (interlocking crystals), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White, gray, or yellowish, Luster: Vitreous to dull, Structure: Granoblastic (interlocking crystals), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together. These deposits can range from Precambrian to relatively recent geological ages.
Uses & applications
Used in construction as crushed stone or road ballast, as a dimension stone for flooring and countertops, and in glass manufacturing if the silica content is high enough.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming ridges or mountain peaks. Unlike sandstone, when quartzite breaks, it fractures through the quartz grains rather than around them.
Field identification & locations
Identify it by its extreme hardness (cannot be scratched by steel) and its granular, sugary appearance. It is commonly found in mountain belts and shield areas like the Appalachian Mountains or the Lake Superior region.
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