Aluminum oxide is also called alumina. Here is a website that contains a whole bunch of oxides.
http://www.galleries.com/minerals/oxides/class.htm
Also, rubies are not strictly aluminum oxide, but a mix of other metals including chromium.
From wikipedia:
Ruby is a red gemstone, a variety of the mineral corundum (aluminium oxide) in which the color is caused mainly by chromium. Its name originates from ruber or rubrum, Latin for red. Natural rubies are exceptionally rare, though artificial ones (sometimes called created ruby) can be manufactured by the Verneuil process relatively inexpensively. Other varieties of gem-quality corundum are called sapphires.
