metamorphic
Quartzite
Quartzite (composed primarily of Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (sometimes pink or red due to iron oxides); Luster: Vitreous (glassy) to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (sometimes pink or red due to iron oxides); Luster: Vitreous (glassy) to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, hard rock. It is found in mountain belts and Precambrian shield areas worldwide.
Uses & applications
Extensively used in construction as crushed stone for road grit, railroad ballast, and building stone. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal. It is also used as a decorative stone in countertops and landscaping.
Geological facts
Quartzite is so hard and durable that it often forms the crests of mountain ridges because it resists weathering better than surrounding rocks. Unlike sandstone, which breaks around its grains, quartzite breaks across its grains due to the total recrystallization of the silica.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. It will not fizz with acid (distinguishing it from marble). Common in places like the Appalachian Mountains, the Alps, and the Lake Superior region.
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