metamorphic
Rounded gray cobble, likely quartzite or fine-grained sandstone
Quartzite (SiO₂), provisional identification
AI-generated identification · may be incorrectLight gray, smooth and strongly weathered/rounded, with a fine granular texture and dull to slightly silky luster; quartzite has Mohs hardness about 7, no cleavage, and specific gravity around 2.65. The image cannot reliably distinguish quartzite from durable sandstone or graywacke.
Identified More metamorphic →
Explore Rounded gray cobble, likely quartzite or fine-grained sandstone in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Light gray, smooth and strongly weathered/rounded, with a fine granular texture and dull to slightly silky luster; quartzite has Mohs hardness about 7, no cleavage, and specific gravity around 2.65. The image cannot reliably distinguish quartzite from durable sandstone or graywacke.
Formation & geological history
Likely a glacially or fluvially transported cobble shaped by abrasion; quartzite forms when quartz-rich sandstone is metamorphosed under heat and pressure, commonly during mountain-building. Its precise geological age and source cannot be determined visually.
Uses & applications
Common quartzite is used as aggregate, roadstone, landscaping rock, and building stone; attractive pieces may be polished or collected but are generally low-value.
Geological facts
Quartzite resists weathering more strongly than most surrounding rocks, so it commonly remains as rounded stream or glacial cobbles. A steel file should not scratch true quartzite; sandstone may show more obvious grains and weaker resistance.
Field identification & locations
Common in streambeds, glacial deposits, beaches, and upland gravels worldwide; inspect a fresh chip for interlocking quartz grains and test with a steel nail/file. Estimated value: $1–$10 as a landscape or field specimen, potentially $10–$30 if unusually attractive and polished.
More like this
