In terms of physical properties, Bauxite formula has a different composition. What it means is that bauxite contains a mixture of oxides like aluminium hydroxides, hydrous aluminium oxides, and minerals like gibbsite, boehmite and diaspore including some clay minerals. It also contains, insoluble materials namely magnetite, quartz, siderite, hematite and goethite. It is usually, yellow, white, beige, grey, reddish-brown, pink and brown. http://www.kingconref.com/mullite/