Coral is a primitive animal, close to the family of jelly that feeds on plankton. The coral grows several mm to several cm per year depending on the species. If some are solitary, most corals grows in an ecosystem called coral colonies. Oldest coral reefs back about 500 million years ago. As colonies, their longevity far exceeds that of quahog clams that can live more than 400 years.
Even though there are many opposite example, corals generally grow in shallow warm seas. Thez indeed need oxygen and light to accomplish photosynthesis, and often stay in area where the sun's rays reach them easily.
There are over 7000 species in very diverse forms and colours. I use the Black Coral, which feels like wood and is very light, Foam Coral, which is much less compact, like the fossilized coral stone by its density. I also use the classic red coral and the beautiful Mediterranean Coral, Example on the picture.