Bauxite is a dark-red sedimentary stone. Once highly prized as the only practical source of magma-safe mechanisms to create magma-proof devices, its importance has declined with the addition of many new heat-resistant forms of stone as well as the ability to make metal mechanisms from iron and steel. Nevertheless, it is still used by some long-time players for nostalgia and its rare, bloody appearance makes it an interesting aesthetic choice.
In real life, bauxite is an ore of aluminum, but the technology required to extract it is beyond the level possessed by dwarves.
 In Real Life
Bauxite is a stone comprised primarily of the minerals gibbsite (Aluminum Hydroxide: Al(OH)3), boehmite (Aluminum Oxide-Hydroxide: γ-AlO(OH)), and diaspore (Aluminum Oxide-Hydroxide: α-AlO(OH)) (none of which are individually present in Dwarf Fortress). Bauxite forms by the weathering and mineralization of various aluminum-rich soils or clays. Despite the correspondence in game, corundum, the mineral that makes up ruby and sapphire (Aluminum Oxide: Al2O3) does not form in bauxite.
Extracting aluminum from bauxite, even in the most primitive way, requires the use of the Hall–Héroult process: the electrolysis of bauxite which has been dissolved into molten cryolite. The development of this process transformed aluminum from an exceptionally rare metal to a cheap, utilitarian material. Dwarves have not yet discovered electricity, therefore they cannot make use of electrolysis to get aluminum from bauxite. (If it were implemented, lightning might work)
[INORGANIC:BAUXITE] [USE_MATERIAL_TEMPLATE:STONE_TEMPLATE] [STATE_NAME_ADJ:ALL_SOLID:bauxite][DISPLAY_COLOR:4:7:0][TILE:'+'] [ENVIRONMENT:SEDIMENTARY:CLUSTER:100] [MELTING_POINT:13600] [BOILING_POINT:15000] [IS_STONE] aluminum can occasionally be found in its free form in environments that like oxygen, volcanic muds were mentioned