Aluminum

A light, silvery metal — uncommon and expensive on Roshar — that Navani's scholars have come to treat with sharp interest. Rushu is mapping its peculiar relationship to paired fabrials: even thin sheets of it block the spanreed link between two halves of a conjoined ruby, severing communication cleanly. The properties suggest it interferes with Investiture in ways the Tower's artifabrians have only begun to chart. SA:DS:Ch 4

An Allomantically inert metal — neither Pushed nor Pulled by steel or iron — and rare enough that it costs more than gold or platinum. A bullet cast from aluminum or one of its alloys is invisible to a Coinshot's blue lines and slips past the defensive Push of a steel bubble, which makes it the obvious round for hunting Allomancers. MB2:AoL:Ch 2

A light silvery Allomantic metal whose description was preserved on the Lord Ruler's plate in the eastern cache — though Vin and Elend already knew of it before reading the plate. MB1:WoA:Ch 5