Do you have a better photo? Can't see it clearly enough to do more than guess.

Gravel?

Concrete with debris all over it. See the debris on the roof as well?

I grabbed this picture online and don’t have a better one unfortunately.

At that angle and distance, it is impossible to tell. Could be crushed white gravel, could be oyster shells, could be concrete, could even be closely fitted pavers.

Debris can collect on any of the above. 😊

Who knows and really the picture shows nothing to give a clue as to what the material is or what you think is so special about it.

Thanks Patricia, this helps.

Thanks @gardengal48 this gives me great ideas to look up. Thanks so much! 😀

Decomposed granite?