metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, with yellowish-brown iron staining in this specimen; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, with yellowish-brown iron staining in this specimen; 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-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together. This specimen appears to contain iron impurities which have oxidized.
Uses & applications
Used extensively in construction as road ballast, roofing tiles, and decorative flooring. High-purity quartzite is also used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, forming resistant ridges. In the Stone Age, it was occasionally used as a substitute for flint to create stone tools, although it is harder to flake.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its granular, sugary texture that resembles sandstone but cannot be rubbed off. It breaks through the quartz grains rather than around them. Common in metamorphic belts worldwide.
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