Red coral is a marine organism that forms the skeletal structure of certain species of coral in the genus Corallium, specifically Corallium rubrum. The skeleton, which is often used in jewelry, has a distinctive red to deep reddish-orange color. Red coral is composed of calcium carbonate and forms in deep, cold waters, primarily in the Mediterranean Sea and around Japan. It has a Mohs hardness of 3.5 to 4, making it relatively soft and best suited for use in beads, carvings, and other ornamental jewelry. Due to overharvesting, red coral is now protected by various conservation efforts in order to preserve coral reefs and marine ecosystems.