metamorphic
Quartz-rich metamorphic rock (probable quartzite)
Quartzite; predominantly crystalline SiO₂, with possible mica and iron-oxide impurities
AI-generated identification · may be incorrectHardness about 7 Mohs; gray-brown, granular, and glassy to dull luster. Interlocking quartz grains produce a massive texture with no obvious cleavage; dark patches may be mica or weathered iron minerals.
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Physical properties
Hardness about 7 Mohs; gray-brown, granular, and glassy to dull luster. Interlocking quartz grains produce a massive texture with no obvious cleavage; dark patches may be mica or weathered iron minerals.
Formation & geological history
Forms when quartz-rich sandstone is recrystallized under high heat and pressure, commonly during mountain building. The specimen’s precise age and locality cannot be determined from the photograph.
Uses & applications
Used as crushed stone, aggregate, paving, countertops, and decorative stone; attractive pieces may be collected, though this small rough fragment has minimal commercial value.
Geological facts
Quartzite commonly breaks across grains rather than around them, making it tougher than sandstone. Dark inclusions can make it resemble a weathered metamorphic or igneous rock.
Field identification & locations
Likely identification requires a hardness test: it should scratch ordinary glass and resist a steel knife; acid should not fizz. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and western North America.
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