Argonite arrowheads are used in the Dungeoneering skill to create arrows. Argonite arrowheads can be smithed from an Argonite bar at level 60 Smithing, yielding 20 Argonite arrowheads and 64 Smithing experience. They can be attached to headless arrows, 15 at a time, to create Argonite arrows.
Making argonite arrowheads is more profitable in a dungeon than selling argonite bars to the Smuggler. Whereas a bar would sell for 1335 rusty coins, the 15 arrowheads made from the bar sell for 133 rusty coins each, so 1995 in total.