metamorphic
Quartz-rich rock, likely quartzite
Quartzite; predominantly microcrystalline quartz (SiO₂), possibly with mica or feldspar impurities
AI-generated identification · may be incorrectHardness about 7 Mohs; gray-brown to tan, granular and massive, with a glassy to dull luster. Quartz grains are interlocked and show no obvious cleavage; specific gravity is approximately 2.6–2.7.
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Physical properties
Hardness about 7 Mohs; gray-brown to tan, granular and massive, with a glassy to dull luster. Quartz grains are interlocked and show no obvious cleavage; specific gravity is approximately 2.6–2.7.
Formation & geological history
Formed when quartz-rich sandstone was metamorphosed under elevated pressure and temperature, recrystallizing the sand grains. Its exact geological age cannot be determined from the photograph and depends on the source formation.
Uses & applications
Used as durable building stone, aggregate, paving, and decorative material; attractive varieties may be polished for specimens or limited lapidary use.
Geological facts
Quartzite commonly breaks across grains rather than around them, making it tougher than ordinary sandstone. Brown coloration can result from iron-oxide staining or weathering.
Field identification & locations
Identify it by testing whether it scratches glass and by examining a fresh fracture for fused quartz grains; dilute acid should not fizz. Common in metamorphic mountain belts worldwide, including the Appalachian and Rocky Mountains.
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