metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together to form a very hard, durable rock.
Uses & applications
Used as a decorative stone in landscaping, as a construction aggregate, for railroad ballast, and in the manufacturing of glass and ceramics due to its high silica content.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them. It is one of the most chemically and physically resistant rocks found on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It is commonly found in mountain folds where tectonic pressure was high. Look for smooth, water-worn pebbles in stream beds.
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