Salt, like any other loose materials, looks like simple triangles in a sketch. To add volume, make the bottom line rounded.
Salt comes in different sizes: from fine to very coarse. You can convey this in a sketch too. For fine salt โ straight lines, for coarse โ jagged ones.
If you add a shadow, the shadow line will be just as uneven as the edges of the heap itself. And a few small crumbs around it will make it look more natural.