Beaches with attractive pebbles

Ok so the title looks odd, but I've recently bought a stone tumbler/polisher for the kids and although you can buy rough pebbles from all over the world, I'd like to try it on some local stones.

Ideally there should be some colour or quartze in them, but can anyone recommend a beach in Cork that may have unusual or 'pretty' pebbles or stones, don't have to be particularly smooth.

thanks