Looks sort of like the dull side of tin foil.
Weapons primarily, since it's not very pretty, and thus not used much for jewelry purposes. It looks like cheap silver, and if you're going to have something that looks like cheap silver, you might as well just have silver, get it scuffed up, and use the lumium in a weapon anyway!
Very soft, extremely rigid, extremely light.
This is classified as "very rare".