Retouched Flake from Nevada

Found very little while exploring around Las Vegas, Nevada. My son found this at the entrance to a canyon about 40 miles north of the city. I think the material is called chalcedony ("cal-said-nee"):
At first I thought it was just a nice flake, then I looked more carefully and noticed additional flaking and use wear along one edge:Here is the back.
At this point you start noticing the dark line across the top of the item, opposite to the used edge. Looks like residual staining from where the item was hafted: a small sharp edge inserted and glued into the lengthwise crack of a stick?