metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or tan with possible reddish/brown streaks; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or tan with possible reddish/brown streaks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or tan with possible reddish/brown streaks; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, usually during mountain-building events (orogenic cycles). The process fuses quartz grains together into a dense, interlocking matrix.
Uses & applications
Used in construction as crushed stone or decorative building stone, in the manufacture of glass and ceramics, and as a durable material for kitchen countertops. Smooth river-worn specimens are popular for landscape gardening.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, leading it to form the crests of many mountain ranges. It is harder than steel and can easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sugary texture. It is commonly found in ancient mountain belts and riverbeds where it has been transported and smoothed by water.
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