In answer, yes, freezing, and just plain erosion can and does cause conchoidal fractured flakes. I frequent many creeks and rivers here in Montana (fishing mostly, but sometimes rockhounding) that are full of different jaspers, cherts, and agates, and these type of "flakes" like you have pictured are more than common. However, Native Americans did use this stuff. And there are quarries here, I rockhound at one known (HUGE) quarry site here for jewlery grade jasper and nodules of druzy quartz in that jasper in a spot that has been quarried for thousands of years. There are literally hundreds of pits where they mined the stuff. This particular spot is ok to rock hound, but any artifacts here are illegal to take according to the Forrest Service that controls that particular land. I personally have also found a spot no one knows about that are obvious pits where a mixture of agate and jasper was "mined" in another area that I discovered while hunting elk, and I have found points 30 miles away from that series of pits, that are made of the exact material, that is distinct from that spot. To answer your question about knapping it, it depends, some jaspers and cherts have to be heat treated to make them knappable. That's the extent of my knowledge on what you might have there. I'm not saying you have found a quarry, but I would say it is possible. It's also possible that it is just an outcrop of jasper. There are others on here with more knowledge than me that might help you further.
