Bauxite is a very common ore which, along with corundum's reasonably high hardness, contributes to corundum's status as a common, inexpensive abrasive.
en.wikipedia.org It is commonly associated with olivine, magnetite, serpentine, and corundum.
en.wikipedia.org It occurs with calcite, ettringite, wollastonite, larnite, brownmillerite, gehlenite, diopside, pyrrhotite, grossular, spinel, afwillite, jennite, portlandite, jasmundite, melilite, kalsilite and corundum in the limestone xenoliths.
en.wikipedia.org Sapphire and ruby are both varieties of the same mineral; corundum.
en.wikipedia.org It largely consists of the mineral corundum (aluminium oxide), mixed with other species such as the iron-bearing spinels, hercynite, and magnetite, and also rutile (titania).
en.wikipedia.org