metamorphic
Rounded quartz-rich cobble, likely quartzite
Quartzite; predominantly SiO₂ (recrystallized quartz)
AI-generated identification · may be incorrectHardness about 7 Mohs; pale gray to tan, granular and weakly banded, with a vitreous to dull luster. Quartzite has interlocking quartz crystals, no obvious cleavage, and high durability; the dark surrounding pavement is likely unrelated asphalt or rock.
Identified More metamorphic →
Explore Rounded quartz-rich cobble, likely quartzite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness about 7 Mohs; pale gray to tan, granular and weakly banded, with a vitreous to dull luster. Quartzite has interlocking quartz crystals, no obvious cleavage, and high durability; the dark surrounding pavement is likely unrelated asphalt or rock.
Formation & geological history
Formed when quartz-rich sandstone was subjected to metamorphic heat and pressure, typically during mountain building; its exact geological age cannot be determined from the image. Rounded edges indicate transport by glacial ice, a stream, or beach processes.
Uses & applications
Used as crushed aggregate, paving stone, building stone, and decorative landscape rock; attractive varieties may be cut or polished. This ordinary cobble has little commercial value.
Geological facts
Quartzite commonly preserves faint original sedimentary layering while becoming much harder than sandstone. It can resemble marble, but quartzite generally does not fizz with dilute hydrochloric acid.
Field identification & locations
Common in regions containing metamorphic mountain belts or glacial deposits, including the Appalachians, Rocky Mountains, and many northern landscapes. Scratch testing with steel may leave no mark; a glass scratch and lack of acid reaction support quartzite identification.
More like this
