Basalt is a volcanic igneous rock with a crystaline structure. It forms when lava rapidly cools.
It can be hard to distinguish from sandstone, especially when weathered, as certain types are lighter brown in colour.
However, its crystaline structure and hardness mean that broken pieces retain sharper angular edges than sandstone and it has a more reflective look to it. The crystaline structure can often be seen on broken surfaces. Basalt is often quite black in colour but can be different shades of brown.