The materials are pretty straight forward.
Small crystal jar or container (this are the only materials that I bought, 1 dollar at a thrift store)
Sea pebbles 1/4" to 1/2" dia. for the bottom
Sea Rocks 1" to 1 1/2" dia. For single top (some of the rocks has small holes in them were seashells use to live, I put a bit of ground moss in them)
2 types of Moss (tree moss and ground moss)