There are all sorts of materials you can use to build fireplace mantels, but don't rule out wood, even if you're into exotic home decor. Wood can be made into interesting shapes by machines, woodworkers, or... the ocean.
Driftwood that is worn smooth and shaped by its journey through the water can be made into unique furniture pieces, and in the case shown here, it can even made a rustic mantel.
The piece shown here is the work of All Driftwood Furniture, and they've got everything from tables to mirrors to lamps to various sculptures made from pieces scrounged from the water.
A nice touch for a rustic home or a beach side cottage.