This boss is technically battled twice. The first encounter is in the Duke's Archives and is impossible to beat. You're supposed to die (you will lose everything as per norm, so I recommend a Ring of Sacrifice if you have a lot of souls on hand.
The second time you encounter him is in the Crystal Caves. The fight is pretty easy since he is a large boss. The general rule of thumb with large bosses is to stay as close to them as possible and hug them to
minimize the chances of being hit. You need to destroy the Primordial Crystal so you can do damage to him. Then hug is front and hit him. He can curse you by breathing crystals on the ground. Simply run as far away as possible to avoid being cursed. Repeat until defeated.