Precious, or red coral is a variety of marine coral known for its durable bright red or pink skeleton that has been used in jewellery making and decorative arts since antiquity. One of the few organic gemstones, red coral grows on rocky sea bottom in tropical or subtropical waters. The species prefers dark environments with low sedimentation, such as deep caverns or crevices. Coral can be found anywhere between 10 and 1,500 meters below sea level, however as of 2019, the shallower habitats have been significantly diminished due to excessive harvesting. Red coral grows in the shape of small skeletal bushes and can reach up to one meter in height. The gemstone is composed of highly pigmented intermeshed spicules of hard calcium carbonate. It has a relative density of 3.86 and hardness 3.5 on the Mohs scale, which indicates a significant fragility of the stone. The skeleton of free growing coral is naturally matte, and it is usually polished for further use.