text: how to tell an arrowhead from an old rock? what about the average size? if the rock in your hand has definite hand chisel marks on it and bears something of a man-made shape, then you may well have found an unfinished arrowhead.  finished arrowheads look like a small 2" or 3" spearhead carved from rock, with indentions cut along either side, close to the bottom to allow the rope tie on the arrow stick.  i used to love searching for and finding arrowheads. the rarest arrowhead is one made from pure crystal; usually, it's the tribal chief's arrowhead.