Metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 (Mohs), Color: Brownish, tan, or gray, Luster: Vitreous to dull, Crystal structure: Massive (interlocking quartz grains), Cleavage: None (conchoidal to uneven fracture)
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Physical properties
Hardness: 7 (Mohs), Color: Brownish, tan, or gray, Luster: Vitreous to dull, Crystal structure: Massive (interlocking quartz grains), Cleavage: None (conchoidal to uneven fracture)
Formation & geological history
Forms from the metamorphism of quartz sandstone under high heat and pressure, typically in tectonic convergence zones.
Uses & applications
Used in construction, decorative stone, railway ballast, and sometimes for producing silica for industrial applications.
Geological facts
Quartzite is exceptionally hard and resistant to chemical weathering, often forming prominent ridges in landscapes.
Field identification & locations
Identify by its hardness (scratches glass), granular but fused appearance, and lack of reaction to acid. Commonly found in areas of past tectonic activity.
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