I would almost say quartzite, but it apparently knaps pretty well. You might try to sharpen your knife on a piece broken flat.
It must knap pretty well, since there are long flakes gouged out of the belly side, one of which is 2/3rds the length of the piece, and only about a half inch wide.
Apologizes if discussion of such simple artifacts offends anyone.
The edges were only sharpened about 2/3rds of the way up the sides. It is sharpened, removing flakes from the polished edge about 2/3rds of the short side edge, and the same on the long side edge. There are no wear marks after sharpening. Each starts being blunted at the same spot on each side. The blunted areas still show the polish and wear from long use. That would suggest is was gripped or hafted in some way on that end, which made little sense to me. I had been trying to figure why the one corner was as polished as it was.
After a little more looking, it appears to have been a hoe or adze, and the blade end was smashed, so they put it to a different use. Guess that explains the polishing from wear. It appears the modifications were done to straighten out the sides to use it as a scraper. The ends of the flakes that made the edge are still there, and so is evidence of the damage. Seems the tool makers who produced these tools liked to end their impact blades with a deep notch, and when the end shattered, it broke to that notch, and drove flakes off both sides.
This picture shows the common notch at the end of the two sharpened areas, and the long flakes from the bottom area too.