Editing Aluminium oxide (section)

==Natural occurrence==
[[Corundum]] is the most common naturally occurring [[crystallinity|crystalline]] form of aluminium oxide.<ref>{{Cite book|url=https://books.google.com/books?id=9WyXTae58DgC&q=Corundum+is+the+most+common+naturally+occurring+crystalline+form+of+aluminium+oxide.&pg=PA46|title=Atomic Layer Deposition Applications 6|last=Elam|first=J. W.|date=October 2010|publisher=The Electrochemical Society|isbn=9781566778213|language=en}}</ref> [[ruby|Rubies]] and [[sapphire]]s are gem-quality forms of corundum, which owe their characteristic colours to trace impurities. Rubies are given their characteristic deep red colour and their [[laser]] qualities by traces of [[chromium]]. Sapphires come in different colours given by various other impurities, such as iron and titanium. An extremely rare delta form occurs as the mineral deltalumite.<ref>{{cite web |title=Mindat.org - Deltalumite |url=https://www.mindat.org/min-47933.html |website=www.mindat.org |publisher=Hudson Institute of Mineralogy |access-date=15 May 2025}}</ref><ref>{{Cite web|url=https://www.ima-mineralogy.org/Minlist.htm|title=List of Minerals|date=21 March 2011}}</ref> Although aluminum is the most abundant metal in the earth’s crust, it must be extracted from bauxite as alumina to produce aluminum metal.<ref name="Myers" />