metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, tan, or gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure causes quartz grains to recrystallize and fuse together into a dense, solid rock. This specimen shows significant rounding from water erosion (alluvial/river transport).
Uses & applications
Used as a decorative stone, in construction as crushed stone for road beds, and in manufacturing silica-based products. Highly durable for outdoor landscaping.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is more resistant to weathering than the sandstone it originated from, often forming the resistant caps of ridges and mountains.
Field identification & locations
Identify in the field by its extreme hardness and the fact that it breaks through quartz grains rather than around them (unlike sandstone). Commonly found in riverbeds, glacial tills, and ancient mountain belts.
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