metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to light grey with a slightly sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular mosaic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale
- Color
- White to light grey with a slightly sugary texture
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light grey with a slightly sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular mosaic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 to 2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the original quartz grains to recrystallize and fuse together into a dense, hard rock. This process can occur over millions of years during mountain-building events.
Uses & applications
Used as a decorative stone in landscaping, as a construction aggregate for road ballast, and in the production of glass and industrial silica. High-quality slabs are used for countertops and flooring.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the capstones of mountains, as it resists erosion much better than surrounding rocks. It is frequently confused with white marble, but unlike marble, it will not fizz with acid and is much harder.
Field identification & locations
Identify in the field by its hardness (it easily scratches glass) and its sugary, granular appearance. It is found in mountain ranges and ancient metamorphic shields worldwide, such as the Appalachians and the Alps.
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