metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 (Mohs scale), Color: light grey to white, Luster: vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: none, Specific gravity: 2.6-2.7.
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to white, Luster: vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: none, Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse together.
Uses & applications
Commonly used as crushed stone for road construction, railroad ballast, and high-quality specimens are used in decorative stone or as a source of silica.
Geological facts
Quartzite is so tough that it often outlasts other rocks during erosion, often forming the caps of ridges and mountains. It will break across the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and granular, sugary texture. Often found in mountain ranges or as water-worn river cobbles.
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