metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White, gray, or yellow/brown (from iron oxidation), Luster: Vitreous to dull, Structure: Granular/crystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White, gray, or yellow/brown (from iron oxidation), Luster: Vitreous to dull, Structure: Granular/crystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in orogenic belts. This specific specimen appears to be a river-worn cobble, smoothed by water transport.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a raw material for glass and ceramics. Polished varieties are used for countertops and landscaping.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is one of the most durable rocks on Earth, often forming the resistant ridges of mountain ranges.
Field identification & locations
Identify by its hardness (7) and the way it breaks through quartz grains rather than around them. Commonly found in riverbeds and mountainous regions globally.
