Okay, so in history obsidian was used as weapons, why not in minecraft! Obsidian could be used for blade weapons and arrows, depending on what you got. As you mined obsidian sometimes you would break it and get shards or arrowheads, which will decide what weapon you can make, and it would be a powerful weapon material. You just mine it like normal just sometimes it would break and give you obsidian weapon pieces, wouldnt that be so cool?
2.Make a "Hardend workbench" (Stone surrounding workbench)
3.One obisidan -> 3 shards
4. Stick + Obsidian shard = knife
5.Knife + obsidian shard = arrowhead (knife looses durability, max 70)
6. PROFIT