metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: White to light pinkish-grey. Luster: Vitreous to dull. Crystal structure: Granular, interlocking quartz grains. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White to light pinkish-grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: White to light pinkish-grey. Luster: Vitreous to dull. Crystal structure: Granular, interlocking quartz grains. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together, creating a hard, durable rock. Geologically can range from billions to millions of years old.
Uses & applications
Used in construction as crushed stone for road beds and railway ballast. Also used as dimension stone for counter tops, floor tiles, and decorative wall coverings. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. Unlike sandstone, which breaks around the grains, quartzite breaks through the quartz grains due to the complete recrystallization.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance. It commonly occurs in folded mountain belts. Collectors look for samples with distinct colors like deep purple or green caused by mineral impurities.
