The dark relic is a possible reward from the Chambers of Xeric. It has a Commune option which will result in the chat box stating A dark power emenates from the relic. You sense that this power can be directed. The player can then receive experience equal to 6,000x (on OSRS it is 150 times the level) the player's level for skills used in the Chambers of Xeric (combat skills, Mining, Woodcutting, Herblore, Farming, Hunter, Cooking, Fishing, Thieving, Firemaking and Agility), and 50x for other skills.
Experience rates:
Normal: 6,000 * level
Hardcore ironman: 1.200 * level
Classic: 750 * level
Elite ironman: 600 * level
Example:
normal mode: level 84 x 6,000 = 504.000 experience, respectively.
hardcore ironman: level 84 * 1.200 = 100.800 experience, respectively.
classic: level 84 * 750 = 63.000 experience, respectively.
Elite ironman: level 84 * 600 = 50.400 experience, respecitvely.