Stone doesn't hold an edge like steel-that's one reason steel is in common use. It depends a lot on the type of stone, too-something like rhyolite or raw chert willl hold an edge longer than softer, heat-treated chert. Like Eddie said, a break often exposes new sharp edges. It's not much trouble to resharpen them, either. You can resharpen hafted points without much work. I carry a really fine-tipped pressure flaker in my hunting stuff, it only takes a minute to run a series of micro-flakes down the edge of an arrowhead to touch it up.
