Red coral, like all coral used as a gem, is not a mineral but the hard skeleton of a colonial marine animal, precious Mediterranean coral being the red Corallium rubrum, built of calcium carbonate secreted by the living polyps. It is soft, hardness 3 to 4, sensitive to acid and heat, and takes a fine polish. Its most important traditional role is in jyotisha, Indian astrology, where under the names moonga or praval it is the gem of Mars, Mangal, and one of the nine navaratna stones, prescribed to strengthen a weak or afflicted Mars for courage, energy and vitality, a living and documented tradition with its own prescriptive literature.
In the Mediterranean world red coral had a long parallel life as an apotropaic charm, worn against the evil eye and hung on children, a use shown in Renaissance painting. An honest account now notes the conservation cost, since precious-coral harvesting depletes slow-growing colonies. Its metaphysical associations largely restate the Martian character in traditional and modern terms.