metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or brownish iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (fractures across grains); 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, often with yellow or brownish iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (fractures across grains); 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 into a solid, interlocking mass of quartz crystals.
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone for flooring or countertops. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics. Also used as a decorative stone in landscaping.
Geological facts
Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the peaks of hills and mountain ridges. It is harder than steel, meaning it will easily scratch a knife blade.
Field identification & locations
Identify in the field by its hardness (it should scratch glass) and its sugary/granular texture. Found in mountain ranges and ancient metamorphic terranes globally. Collectors often look for examples with unique color patterns or mineral inclusions.
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