metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, or reddish-brown; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, or reddish-brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, or reddish-brown; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. It can be found in mountain ranges and areas with ancient continental crust.
Uses & applications
Used as a decorative stone in landscaping, crushed stone for road construction, and occasionally for high-durability kitchen countertops or jewelry when high purity.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of ridges and mountains. It is harder than steel and cannot be scratched by a knife blade.
Field identification & locations
Identify by its hardness (will scratch glass) and lack of reaction to acid. It has a sugary or grainy appearance but breaks across the grains rather than around them. Common in glacial till and riverbeds.
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