What can I do with a whole load of mussel shells?

[thehouseofmirth]

I've got about 3 carrier bags full of them and can't think of anything to do with them but can't bear to throw the away. I feel sure I ought to be able to do something with them on the allotment or garden but what?!

Bleach them and use them in the garden borders or on top of pot plant soil?

My friend used them as a mulch for potted plants to stop weeds growing, and they looked lovely - unusual and different.