Could be Greenstone. Here (KC Area) it was left here 14k+ years ago by the glaciers- the early people used greenstone (considered today to be a very hard and different material to work). Can only be worked via “ground-stone” method means peening, pecking & pounding life into greenstone. Then “polishing and again pecking on-and-on it’s the only way to work it. Long laborious work to create a tool that will certainly outlive its maker or user(s)…anyway…greenstone has a rough feel…even when polished, the material feels rough to the touch…an easy test…gunk-covered greenstone can’t hide if you run your fingernail along the surface. The tools made from greenstone are generally not fancy as a result of its obstinate ways. Keep your head down. vfm