If a mass of granite is in contact with a layer of sandstone that contains small pieces of the granite, which rock is older?

The granite

Explanation:

Sandstone forms when the granite slowly crumbles due to wind and rain. For this reason we can say that granite is the oldest rock.

The granite quartz grains form the sand. Sands and sand dunes, but they are not rocks: they are fragments of rocks. The sand may settle on the sea floor or in depressions and be subjected to increased pressure or temperature. Thus cemented and hardened, it forms sandstone - a type of sedimentary rock. Sandstone is used in floors.