metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with earthy weathering; Luster: Dull to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or white with earthy weathering
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with earthy weathering; Luster: Dull to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, typically in orogenic (mountain-building) belts.
Uses & applications
Used as a decorative stone in landscaping, crushed stone for road construction, and higher quality slabs for kitchen countertops and flooring due to its extreme durability.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, leading to the formation of prominent ridges and peaks. Unlike sandstone, when quartzite breaks, it fractures through the sand grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for a granular texture that appears fused. Frequently found in riverbeds as rounded 'river rocks'.
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