metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: white, grey, or yellowish. Luster: Vitreous to dull. Crystal structure: Hexagonal/trigonal (microcrystalline grains). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- white, grey, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: white, grey, or yellowish. Luster: Vitreous to dull. Crystal structure: Hexagonal/trigonal (microcrystalline grains). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. Found in mountain-building belts and ancient shield areas.
Uses & applications
Used as decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacture of glass and ceramics due to high silica content.
Geological facts
Quartzite is so hard and durable that it often survives intense weathering to form the ridges of many mountain ranges. It is significantly harder than the sandstone it originates from and will scratch steel easily.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sandpaper-like surface that doesn't rub off. Unlike marble, it will not fizz when exposed to acid.
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