Humm tell me what you think about this. While it's safe to assume that there is some amounts of metals that they have access too (say gold, silver and bronze) they have to import Iron from other places (the only iron mines were on the far west end of Tarth so they lost all they had) but they have a few other things that are avalible since it's a "fantasy" setting. For one they can make armor out of Chittin since there are giant insects in the deserts. And they have a type of special glass, made out of special sand, that's harder then normal glass but still not as good as metal but it's sharper then metals. So, for example, an arrowhead made of this stuff will cut through leather armor realy well but would be all but useless aginst heavy armor (like plate) the arrowhead would shatter on impact. On the plus side armor like chainmail (unless woven realy tight) will be less effective against this since the arrow head would break in parts where the links are and the rest of the arrow would go through the hole. Also small blades like knives would be a common product of this. Swords and blunt objects would be made too but they have a certain chance of shattering when being hit by blunt objects (like maces or when being blocked by shields). They would be light weight too so sailors like to use them.