The seventh crystal is in the land of Serkesh (not sure if i remember the name right). You probably went straight into his dungeon, instead of looking for the seventh dungeon. Explore the map a bit, it can't be far.
And i agree on the swords part, they break way too fast, especially when you fight those armoured skeletons. You could try to repair the sword yourself, but it will lose durability everytime you fail to repair it correctly.
__________________
|