I would say that is a "quarry blank" - a roughly worked piece fashioned at a source of stone for transport or trade, and ultimate reduction to a finished artifact. Several years ago there was a site near Exton, Pennsylvania (now obliterated by a housing development) where large quartzite blanks like yours were readily found, albeit almost always broken. The site had local outcroppings of quartz, but not of quartzite. The quartzite was brought in as quarry blanks, and then fashioned into points and knives, some of which finished pieces we would find as well. Some of the quartzite could be identified as coming from the area around Reading, Pennsylvania ( a good 40 miles or so from this site), and I suspect the rest of the quartzite also was carried in from some distance.
artorius