metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 on Mohs scale; Color: typically white to gray; Luster: vitreous to dull; Crystal structure: trigonal (granular); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray; Luster: vitreous to dull; Crystal structure: trigonal (granular); Specific gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing quartz grains to recrystallize and fuse into a solid network. Often found in orogenic belts (mountain ranges).
Uses & applications
Used extensively in road construction, as railway ballast, for floor tiles, and as a decorative stone in landscaping and counter tops.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, meaning it often forms the crests of mountain ridges. It is often confused with marble but is much harder.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and granular, sugary appearance. It will break across quartz grains rather than around them.
