I always had a strange fascination with the decorative soaps my mother would keep out in our bathroom as a child. Most were in the shape of different shells. I really wanted to use them (especially this really dark brown one, which I thought was such a strange colour for soap), but at the same time didn't want to ruin them. She "preserved" them by keeping them in their plastic. I think at one point I snuck one out of the very bottom of the "display" to use in secret. Also they really remind me of the Belgian chocolate sea shells you can buy, which is maybe why I get a strange sort of satisfaction when I bite into one of those.
I found these soaps on etsy which look like big chunks of amethyst or amber. I like the idea of using a soap like this every day, not just hermetically sealed for display.