metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: yellow, tan, orange, or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None, conchoidal to irregular fracture; Specific gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- yellow, tan, orange, or reddish due to iron oxides
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: yellow, tan, orange, or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None, conchoidal to irregular fracture; Specific gravity: 2.6-2.65
Formation & geological history
Quartzite forms from the metamorphism of quartz-rich sandstone under intense heat and pressure. The individual quartz grains recrystallize into an interlocking mosaic, creating an extremely hard and durable rock. It is found in mountain belts worldwide, often dating back to the Proterozoic or Paleozoic eras.
Uses & applications
Commonly used as crushed stone for road construction, railway ballast, and as a decorative stone in architecture. High-purity quartzite is used to produce silica sand for glassmaking and industrial silicon.
Geological facts
Quartzite is so hard that it will scratch glass and steel. In prehistoric times, it was occasionally used as a substitute for flint to create stone tools like scrapers and projectile points because of its durability.
Field identification & locations
Identify in the field by its sugary surface texture and extreme hardness. Unlike limestone, it will not fizz with acid, and unlike sandstone, it does not break around the grains but through them. Found in ancient mountain ranges and areas of high tectonic activity.
