metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, white, or light brownish; Luster: Vitreous to dull; Crystal structure: Trigonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.6–2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, white, or light brownish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, white, or light brownish; Luster: Vitreous to dull; Crystal structure: Trigonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.6–2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. Primarily found in mountain belts or cratonic shields.
Uses & applications
Used as a decorative stone in construction, counter tops, railroad ballast, and crushed stone for road construction. Some high-purity varieties are used to produce silica sand for glass making.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in mountainous areas, forming the sharp peaks. It was used by prehistoric humans to create stone tools because of its durability and sharp edges when broken.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks across individual grains rather than around them. It is very resistant to chemical weathering.
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