metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to white with slight translucency, Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to white with slight translucency, Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause original quartz grains to recrystallize and fuse together. Can range from Precambrian to Cenozoic in age.
Uses & applications
Used in construction as road ballast, roofing granules, and decorative stone. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal.
Geological facts
Quartzite is so tough that it often breaks through the constituent quartz grains rather than around them, unlike sandstone. It is frequently more resistant to weathering than the surrounding rock, often forming ridges or hilltops.
Field identification & locations
Identify by its extreme hardness (scratches glass/steel) and granular, sugary texture. Common in mountain ranges and eroded glacial deposits such as riverbeds or beaches. Often confused with marble, but quartzite will not react with acid.
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