Corundum is a mineral composed of aluminum oxide (Al₂O₃). It was named corinvindum in 1725 by John Woodward, a term derived from the Sanskrit word kuruvinda. In gemology, corundum has two main varieties: ruby (red) and sapphire (blue). Ruby, or carbuncle, is a mineral of class 04 (oxides), according to the Strunz classification. It is a reddish gemstone; if it is purple, it is called balaje. Its color comes from the metals iron and chromium with which this variety of corundum (aluminum oxide, Al₂O₃) is associated. Its name comes from ruber, which means 'red' in Latin.