metamorphic
Rounded metamorphic cobble, likely quartzite
Quartzite; predominantly microcrystalline quartz (SiO₂), possibly with mica or feldspar
AI-generated identification · may be incorrectHardness about 7 Mohs; gray-brown, weathered surface with a dull to weakly sugary luster and faint granular banding. Dense, tough, and lacking obvious cleavage; the rounded shape indicates water abrasion or prolonged transport.
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Physical properties
Hardness about 7 Mohs; gray-brown, weathered surface with a dull to weakly sugary luster and faint granular banding. Dense, tough, and lacking obvious cleavage; the rounded shape indicates water abrasion or prolonged transport.
Formation & geological history
Quartzite forms when quartz-rich sandstone is recrystallized under heat and pressure during regional metamorphism, commonly from Precambrian to younger mountain-building events. The specimen was likely eroded from bedrock and rounded in a stream or shoreline environment.
Uses & applications
Common quartzite is used as aggregate, road stone, riprap, and building or paving stone; attractive varieties are used decoratively. This piece has modest collector value unless its provenance or texture is distinctive.
Geological facts
Quartzite commonly breaks across quartz grains rather than around them, producing a very hard fracture surface. It can resemble chert, sandstone, or weathered granite in hand specimens.
Field identification & locations
Look for sand-sized quartz grains fused into a hard mass, resistance to scratching by a steel blade, and no reaction to dilute hydrochloric acid. Common in metamorphic mountain belts and abundant as durable stream gravels worldwide.
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