Red Sponge Coral 10mmDeep to medium colors of red throughout this gemstone. Red Sponge Coral is not actually made of sponge. It is a unique type of coral, unlike other varieties of coral. It has a sponge like appearance due to small holes that cover the surface. It has a matte red color with no luster or shine which is how it is found in the ocean. Red Sponge Coral is produced by small sea creatures called polyps. Red Sponge Coral can be found in Queensland, Australia,