This cool one glows in sections under a UV  ( aka Black light )

Landscaping  Art deco aquariums terrarians etc

Weights are approximate

First pictures are taken dry

last ones are wet to show how they look in a aquarium with water

You can also soak in Vinegar 24 hours then use a soft bristle brush to remove more of the outside grit

Careful edges are sharp use fine grit sandpaper around edges or nail file