metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with tan and brownish iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with tan and brownish iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with tan and brownish iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure causes the original quartz grains to recrystallize and fuse together into a dense, hard rock. This specimen shows signs of river-rounding (alluvial transport).
Uses & applications
Used as crushed stone for road construction and railway ballast; due to its hardness and resistance to weathering, large boulders are often used in landscaping and riprap.
Geological facts
Quartzite is so tough that it often survives intense weathering that breaks down surrounding rocks. It is harder than steel and will easily scratch glass. The tan/orange patches on this specimen are caused by iron oxide staining.
Field identification & locations
Identify by its ability to scratch glass and its granular, sugary texture that resembles sandstone but will not rub off. Common in mountainous regions or as river cobbles. Look for it in high-energy stream beds.
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