metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-tan to light brown (due to iron staining); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (breaks with conchoidal or uneven fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-tan to light brown (due to iron staining)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-tan to light brown (due to iron staining); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (breaks with conchoidal or uneven fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure. The original quartz grains recrystallize and fuse together into a dense, crystalline mass. It is found in mountain-building belts and ancient continental shields.
Uses & applications
Used as crushed stone for road construction and railway ballast; in manufacturing glass, ceramics, and abrasives. High-purity quartzite is used in the production of metallic silicon.
Geological facts
Quartzite is so durable that it often remains as the caprock of ridges and mountains long after softer surrounding rocks have eroded away. It is significantly harder and more weather-resistant than its parent rock, sandstone.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of foliation. Unlike sandstone, quartzite breaks through the quartz grains rather than around them, resulting in a smoother, glassier surface on fresh fractures.
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