Carbuncle. A beautiful gem of a deep red color (with a mixture of scarlet), found in the East Indies. When held up tot he sun, it loses its deep tinge, and becomes of the color of a burning coal. The carbuncle of the ancients is believed to have been a garnet. The name is now given also to the ruby sapphire and the red spinel. The ordinary carbuncle is a garnet cut en cabochon.