When you reach the point where you have to fight Trolls at Skull Gorge, upgrade your weapons. The best way to do so is to have two maces that can be upgraded. When you upgrade, use these stones for the weapons. With these weapons in hand as you enter Skull Gorge, you should have no problem defeating the Trolls that are waiting there.
Fine Lite Mace: 1 Rune Stone 1 Jancinth and 1 Jade. Combine all these on this one mace and you will have a Mace that will have the Fire and Acid ability and also have a +1 rating as well (Acid damage +1-4 and Fire damage is +1-8).
Fine Morning Star: 1 Rune Stone 1 Ruby. Combine these to create a +1 weapon that will bleed 1 round per level of the character using it.