metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but often pink or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: interlocking grains of quartz; Cleavage: none (fractures across grains)
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but often pink or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: interlocking grains of quartz; Cleavage: none (fractures across grains)
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure (metamorphism). This process causes the original quartz grains to recrystallize and fuse into a solid, hard rock.
Uses & applications
Used as a decorative stone in construction (countertops, wall cladding), for railway ballast, as a raw material for glass manufacturing, and as a durable outdoor flagstone.
Geological facts
Quartzite is so hard that it can scratch steel and glass. It is often confused with marble, but marble will react with acid and is much softer. Due to its resistance to erosion, it often forms the caps of ridges and mountains.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will scratch a steel knife blade). Look for fractures that cut through the grains rather than around them, which distinguishes it from sandstone.
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