Sponge coral correctly known as melithaea ochracea is a natural coral that's freely traded because it's not considered to be endangered. Being porous and very soft can make it challenging to work with so it's not seen that often as a gemstone. Most sponge coral has been stabilized because its natural tree-like structure is full of tiny holes which were once created by polyps. When stones are stabilized they're filled with a resin or other substance to stop them from eroding or crumbling but this can also be a way of strengthening or repairing the material so that it may be used for another purpose.
Whilst not being worn we recommend this sponge coral pendant be covered with a soft piece of material or it can be stored in the pouch that comes with it. As well as protecting the gemstone from unwanted marks and scratches, this will also help minimise any build-up of tarnish on the sterling silver setting.