metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale. Color: Light grey, translucent to opaque with iron oxide staining (brownish-yellow). Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline/interlocking grains). Cleavage: None (conchoidal to uneven fracture). Specific gravity: 2.63-2.65.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale. Color: Light grey, translucent to opaque with iron oxide staining (brownish-yellow). Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline/interlocking grains). Cleavage: None (conchoidal to uneven fracture). Specific gravity: 2.63-2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse into a tough, durable rock network.
Uses & applications
Used as crushed stone in construction, railway ballast, decorative landscaping rock, and historically for making stone tools due to its hardness and fracture properties.
Geological facts
Quartzite is so hard and cohesive that when it breaks, it fractures right through the quartz grains rather than along the boundaries between them, unlike sandstone.
Field identification & locations
Field identification: Scratches glass easily, does not react with acid, and shows fused interlocking quartz grains. Widely found worldwide in mountainous metamorphic terrains.
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