metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown due to iron oxide staining; Luster: Vitreous to dull (weathered); Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown due to iron oxide staining
- Luster
- Vitreous to dull (weathered)
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown due to iron oxide staining; Luster: Vitreous to dull (weathered); Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (fractures across grains); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original sand grains to recrystallize and fuse together. This specimen appears to be a river-worn or glacial cobble, rounded by mechanical abrasion over thousands of years.
Uses & applications
Used frequently as crushed stone for road construction, railroad ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce glass and metallic silicon.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains. Unlike sandstone, which breaks around its grains, quartzite is so well-fused that it breaks through the grains themselves.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary texture on a fresh break. Commonly found in ancient mountain belts and as rounded cobbles in riverbeds or glacial tills.
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