metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: light gray to white; Luster: vitreous to dull; Crystal structure: hexagonal crypto-crystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- light gray to white
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: light gray to white; Luster: vitreous to dull; Crystal structure: hexagonal crypto-crystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together, typically in orogenic (mountain-building) belts.
Uses & applications
Used in construction as crushed stone or decorative facing, in track ballast for railroads, and as a source of silica for glass manufacturing and industrial abrasives.
Geological facts
Quartzite is so hard and durable that it often forms the crests of mountain ridges because it resists erosion better than the surrounding rocks. When broken, it fractures through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its grainy, sugary appearance despite its extreme toughness. Found worldwide in ancient mountain ranges.
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