Carbuncle
CARBUNCLE, a red or fiery-colored precious stone. The carbuncles of the ancients were prob. mainly garnets (NEB Isa 54:12) and, to a lesser extent, rubies (q.v.). The term is now applied to garnet cut in boss shape, usually hollowed out to allow the color of the stone to be seen. The deep-red transparent precious garnet is mainly almandite iron aluminum silicate but in parts is pyrope (magnesium aluminium silicate). Almandite is a common mineral in metamorphic rocks, such as mica schist and gneiss. Pyrope occurs in ultra-basic igneous rocks such as serpentinite.