Wiki - Crystal Caverns
Part 1: Collecting Crystal Samples
Arlin The Geologist has run into some trouble in the Crystal Caverns and is asking for help. Travel to the Caverns and gather 10 Crystal Shards off the Crystal Elementals that live there. Return to Arlin to progress the quest.
Part 2: Defeating The Giant
Arlin sends you back to the Crystal Caverns to deal with the Crystal Giant you probably noticed during your first visit. Defeat it and recover his Satchel. Return it to him to earn a reward for this quest. Rewards can be seen in Arlin's Tent.