alumina vs. aluminum

the natural or synthetic oxide of aluminum, Al 2 O 3 , occurring in nature in a pure crystal form as corundum.

Chemistry.,  a silver-white metallic element, light in weight, ductile, malleable, and not readily corroded or tarnished, occurring combined in nature in igneous rock, shale, clay, and most soil: used in alloys and for lightweight utensils, castings, airplane parts, etc. alum.; Al; 26.98; 13; 2.70 at 20°C.

of, relating to, or containing aluminum.