metamorphic
Quartzite
Metamorphosed Sandstone (SiO2 dominant)
Hardness: 7 (Mohs scale), Color: Grayish-tan with dark inclusions, Luster: Dull to vitreous when wet, Structure: Granular/crystalline, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Grayish-tan with dark inclusions, Luster: Dull to vitreous when wet, Structure: Granular/crystalline, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic activity cause quartz grains to recrystallize and fuse together.
Uses & applications
Used as a high-quality building material, railway ballast, road aggregate, and for decorative landscaping or historical toolmaking.
Geological facts
Quartzite is so durable that it often remains as caps on mountains because it resists weathering better than surrounding rocks. It was famously used for stone tools by Neolithic humans.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found as rounded river stones or in large mountainous outcrops.
