If you've been exploring the Living Lands thoroughly in , there's a good chance you stumbled across some precious Starmetal fragments and are eager to put them to use.
Unfortunately, you won't figure out what they're used for until the last major area, Galawain's Tusks. There are four Starmetal fragments in Avowed, with one in each region.
Once you reach Solace Keep in Galawain's Tusks, you'll find a dwarven blacksmith who can actually put these Starmetal fragments to use.
Forgemaster Dela can turn your Starmetal into two unique weapons — the Moonstrike arquebus and/or the Meteor Blade. If you're short on Starmetal fragments, you'll have to decide which of these unique weapons in is the better option.
This will depend on your build and playstyle, of course, and both the sword and arquebus are among the best in the game for each of their respective weapon types, so choose wisely.