metamorphic
Quartzite
SiO2 (Metamorphosed Sandstone)
Hardness: 7 Mohs scale; Color: Tan, brown, or grey; Luster: Dull to vitreous; Crystal structure: Trigonal/Hexagonal microcrystalline; Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs scale
- Color
- Tan, brown, or grey
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, brown, or grey; Luster: Dull to vitreous; Crystal structure: Trigonal/Hexagonal microcrystalline; Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the original quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used extensively in road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica for glass making.
Geological facts
Quartzite is so tough that it often outlasts the rock surrounding it, frequently forming the tops of ridges and mountains. It breaks across grains rather than around them.
Field identification & locations
Identified by its high hardness (scratches glass) and grainy, sugary texture. Commonly found in ancient mountain belts and riverbeds as rounded cobbles.
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