I've posted about hikaru dorodango a couple times before but they're always worth another look. Dorodango start out as sloppy mud balls but through careful shaping and polishing with dirt and sand, they end up perfectly round and shiny. Here is a particularly beautiful and unusual example, made from some yellow soil in New Mexico:
That totally looks like leather! Here is a more traditional (and shiny!) example:
Both of these were made by dorodango artist Bruce Gardner. Here's some video of how the balls are made:
This video is good as well but if you want to create your own, these detailed directions will be a better guide.