metamorphic
Quartzite
SiO2 (Silicon Dioxide)
Hardness: 7 on Mohs scale; Color: tan to light grayish-brown; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Grain: granular and sugary texture; Specific gravity: approx 2.65.
- Hardness
- 7 on Mohs scale
- Color
- tan to light grayish-brown
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan to light grayish-brown; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Grain: granular and sugary texture; Specific gravity: approx 2.65.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (regional metamorphism), causing the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used as a crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics. Also used as a decorative stone in architecture and landscaping.
Geological facts
Quartzite is so hard and durable that it often forms the ridges and peaks of mountain ranges because it resists weathering better than the surrounding rocks. When quartzite breaks, it fractures through the quartz grains, unlike sandstone which breaks around them.
Field identification & locations
Identify by its high hardness (it will easily scratch glass) and its sugary, crystalline appearance on fresh surfaces. It is commonly found in metamorphic mountain belts globally. To differentiate from sandstone, look for a smooth break across grains rather than a gritty surface.
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