metamorphic
Tumbled quartz-rich pebble (likely quartzite)
Quartzite; predominantly microcrystalline quartz (SiO₂)
AI-generated identification · may be incorrectHardness about 7 Mohs; off-white with gray-brown staining, dull to weakly glassy luster, and no obvious cleavage. Dense, fine-grained, and rounded from natural or human tumbling; visible cavities may indicate weathered impurities or a porous silica-rich rock.
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Physical properties
Hardness about 7 Mohs; off-white with gray-brown staining, dull to weakly glassy luster, and no obvious cleavage. Dense, fine-grained, and rounded from natural or human tumbling; visible cavities may indicate weathered impurities or a porous silica-rich rock.
Formation & geological history
Quartzite forms when quartz-rich sandstone is recrystallized under heat and pressure during metamorphism, commonly from Precambrian to younger mountain-building events. The rounded shape reflects stream abrasion or tumbling.
Uses & applications
Used as aggregate, road stone, building stone, and decorative landscaping material; attractive pieces may be collected or polished. This small specimen generally has minimal commercial value.
Geological facts
Quartzite commonly resembles quartz, but its interlocking grain texture and lack of individual crystal faces distinguish it from a single quartz crystal. Iron-oxide staining can produce cream, tan, or rusty patches.
Field identification & locations
Common in mountain belts and stream gravels worldwide; major sources include the Appalachian, Rocky, and metamorphic belts globally. Test with a steel knife or glass: genuine quartzite should scratch glass and resist a knife, though surface weathering can affect results.
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