metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, typically white, gray, or pinkish in color, vitreous to greasy luster, massive crystal structure with interlocking quartz grains, conchoidal fracture, and specific gravity around 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically white, gray, or pinkish in color, vitreous to greasy luster, massive crystal structure with interlocking quartz grains, conchoidal fracture, and specific gravity around 2.65.
Formation & geological history
Formed from quartz-rich sandstone subjected to high temperatures and pressures through regional or contact metamorphism, often taking millions of years in deep crustal environments.
Uses & applications
Used in construction, as crushed stone for roads, for railroad ballast, in manufacturing refractory bricks, and occasionally as decorative stone or in countertops.
Geological facts
Because quartz is extremely resistant to weathering, quartzite ridges often form prominent hills or mountain ranges as the surrounding softer rocks erode away.
Field identification & locations
Can be identified in the field by its extreme hardness (scratches glass easily), lack of reactivity with acid, and the way it breaks across the quartz grains rather than around them, unlike sandstone.
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