metamorphic
Blue-gray quartz-rich rock, likely quartzite
Quartzite; predominantly microcrystalline quartz (SiO₂), possibly with mica or feldspar
AI-generated identification · may be incorrectTypically Mohs hardness 7, gray to bluish-gray color, vitreous to sugary sparkle, interlocking granular texture, and no obvious cleavage; specific gravity about 2.6–2.7. The image’s polished or naturally worn surface shows abundant reflective grains, but exact identification requires a fresh break and testing.
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Physical properties
Typically Mohs hardness 7, gray to bluish-gray color, vitreous to sugary sparkle, interlocking granular texture, and no obvious cleavage; specific gravity about 2.6–2.7. The image’s polished or naturally worn surface shows abundant reflective grains, but exact identification requires a fresh break and testing.
Formation & geological history
Quartzite forms when quartz-rich sandstone is recrystallized under heat and pressure during metamorphism, commonly during mountain building. Its age depends on the source sandstone and metamorphic event; specimens may range from Precambrian to much younger.
Uses & applications
Used as durable building stone, aggregate, paving, countertops, and decorative stone; attractive pieces are collected or polished. It is generally less valuable than gem-grade quartz specimens.
Geological facts
Quartzite can resemble quartz-rich granite or chert, but its quartz grains are typically fused into a hard mosaic. A steel nail should not scratch it, while quartzite readily scratches ordinary glass.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, Rocky Mountains, Alps, India, Brazil, and Scandinavia. Confirm with a hardness test, acid test, and examination of grain boundaries; the photograph alone cannot establish a precise species.
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