metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow/brown (if stained by iron); Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or yellow/brown (if stained by iron)
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow/brown (if stained by iron); Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact 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 metamorphic belts worldwide, dating from the Precambrian to more recent eras.
Uses & applications
Used in construction for road ballast, roofing tiles, and flooring. Highly crushed quartzite is used in glass making. Due to its resistance to chemical weathering, it is used for laboratory countertops and decorative stones.
Geological facts
Quartzite is so tough that unlike sandstone, which breaks around the grains, quartzite breaks through the grains when struck. It is one of the most durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline texture. It often possesses a grainy appearance but feels very smooth to the touch compared to sandstone. It is ubiquitous in mountainous regions.
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