metamorphic
Quartzite
Metamorphic rock predominantly composed of Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pale green; Luster: vitreous to waxy; Crystal structure: interlocking mosaic of quartz crystals; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or pale green
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pale green; Luster: vitreous to waxy; Crystal structure: interlocking mosaic of quartz crystals; Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, hard rock. Typically associated with tectonic plate boundaries and mountain-building events.
Uses & applications
Used as decorative stone in architecture, as crushed stone for road construction and railway ballast, and occasionally for high-silica glass manufacturing. Pure varieties are collected for their aesthetic crystalline texture.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists weathering better than the surrounding rock. It is often confused with marble, but can be distinguished because quartzite will scratch glass while marble will not.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel blade) and its grainy, crystalline appearance which resembles recrystallized sugar. Found in metamorphic terrains like the Appalachian Mountains or the Scottish Highlands.
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