metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, tan, or yellowish-white, Luster: Vitreous to dull, Structure: Granoblastic, Cleavage: None, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White, gray, tan, or yellowish-white, Luster: Vitreous to dull, Structure: Granoblastic, Cleavage: None, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure. This process recrystallizes the quartz grains, locking them together into a very hard and durable rock.
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, wall coverings, and countertops. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming prominent ridges and hills. When it breaks, it fractures through the quartz grains rather than along the boundaries between them.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and sandy, sugary texture on fresh surfaces. It is found globally in mountainous regions where tectonic activity has occurred.
