metamorphic
Quartz-rich metamorphic rock (likely quartzite)
Quartzite; predominantly crystalline quartz (SiO₂), possibly with mica or feldspar impurities
AI-generated identification · may be incorrectTypically Mohs hardness 7, pale gray to white, and vitreous to sugary luster. Interlocking quartz grains give it a granular texture, conchoidal-to-uneven fracture, and little or no cleavage; the image is also consistent with minor mica-rich foliation or weathering.
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Physical properties
Typically Mohs hardness 7, pale gray to white, and vitreous to sugary luster. Interlocking quartz grains give it a granular texture, conchoidal-to-uneven fracture, and little or no cleavage; the image is also consistent with minor mica-rich foliation or weathering.
Formation & geological history
Forms when quartz-rich sandstone is recrystallized under heat and pressure during regional or contact metamorphism, commonly during mountain building. Its age depends on the original sandstone and metamorphic event, ranging from Precambrian to recent orogenic belts.
Uses & applications
Used as crushed aggregate, road stone, railroad ballast, decorative building stone, and silica feedstock; attractive pieces are collected or polished.
Geological facts
Quartzite is generally harder and more resistant than its sandstone precursor and commonly breaks across, rather than around, individual grains.
Field identification & locations
Identify it by testing whether a steel blade fails to scratch it and by checking that broken surfaces cut through fused quartz grains; acid produces no reaction. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and Indian shield.
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