Adamant bars are used in the smithing skill to create adamant armour and weapons. When smithing, each adamant bar used gives 62.5 smithing experience. Adamant armour and weapons require smithing levels in the range of level 70 (adamant dagger requirement) to level 88 (adamant platebody requirement).
Adamant bars are obtained through smelting adamantite ore. Level 70 smithing and six coal is required per adamantite ore to create a bar which grants 37.5 smithing experience.
Noted adamantite bars are a common drop from Aviansies found within the God Wars Dungeon making them a a very profitable monster to kill.