metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White to yellowish-tan, Luster: Vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to yellowish-tan, Luster: Vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the quartz grains to recrystallize into an interlocking mosaic of crystals.
Uses & applications
Used in construction as crushed stone or road ballast, as a decorative building stone, in high-end countertops, and for manufacturing glass and silica-based ceramics.
Geological facts
Quartzite is so tough and resistant to weathering that it often forms the tops of ridges and mountains. It is significantly harder than the sandstone it originates from.
Field identification & locations
Identify in the field by its hardness (scratches glass) and its tendency to break across the quartz grains rather than around them. Often found in mountainous regions or ancient shield areas.
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