Likely weathered quartzite pebble

Hardness about 7 Mohs; tan-brown, rounded, dull to faintly vitreous luster, with a dense granular texture and no obvious cleavage. The dark patches may be iron-oxide staining or surface weathering.

Quartzite forms when quartz-rich sandstone is recrystallized under metamorphic heat and pressure, commonly during mountain-building; its exact geological age cannot be determined from the photograph. The rounded shape indicates abrasion in a stream, beach, or glacial deposit.

Used as durable aggregate, road stone, landscaping material, building stone, and occasionally as a lapidary or teaching specimen. This small common pebble has minimal commercial value.

Quartzite is typically harder and more resistant to weathering than the sandstone from which it formed. A steel file generally will not scratch it, while quartzite can scratch ordinary glass.

Common in metamorphic mountain belts and derived gravels worldwide. Confirm identification by testing for glass-scratching hardness and looking for fused quartz grains; a vinegar test should show no reaction.