Ore is metals or minerals that are not or cannot be smelted.
Another uncommon ore, copper is used to make a variety of tools- the copper knife, sword, axe, and pickaxe. However, copper is most commonly used to craft bronze, a stronger tool. Due to this, many players consider copper useless because it can be easily skipped over to the bronze tier tools.
Most likely the most underused ore, sulfur is usually(and only) used for making bombs. However, since it only spawns on 2 islands (sulfur/arches) and many players don't usually head there, sulfur is rarely seen. Before bombs exploded, this ore was considered completely useless and a waste of time.
The strongest and the most difficult to obtain, mithril is used by experienced players all around. It is used to make the mithril knife, sword, pickaxe, and axe. It only spawns on 3 locations: The Arches, the Lone Mountain, and in the secret cave on the Mainland. The Arches contain the most mithril, however, the secret cave is the most conveinent.