metamorphic
Quartzite
Quartzite (mainly SiO2)
Hardness: 7 (Mohs scale), Color: Pinkish-red to brownish-grey, Luster: Vitreous to dull, Crystal structure: Trigonal/Hexagonal (granular), No cleavage, Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Pinkish-red to brownish-grey, Luster: Vitreous to dull, Crystal structure: Trigonal/Hexagonal (granular), No cleavage, Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, often during mountain-building events. These specimens appear to be river-worn or beach-tumbled pebbles.
Uses & applications
Used as decorative stones, in landscaping, as a source for silica in glassmaking, and crushed for road ballast or railway bedding.
Geological facts
Quartzite is so hard that it can scratch steel and glass. It is often more resistant to weathering than the surrounding rock, leading to the formation of ridges and hilltops.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. Common in ancient mountain belts and as durable pebbles in riverbeds.
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