I purchased a bunch of casting equipment/lead from a guy a couple of weeks ago. In the box with some cast boolits and fishing weights was a block that I can't identify. He had no idea what it was either. It is 4.25 x 2.25 x .75 in size, very dark grey, and seems to be much harder that the ingots I have around here. I tried the thumbnail hardness tester (I'm not sure if my thumbnails have been calibrated recently), and it seems to be much harder than the WW or #2 ingots I have on hand. I strike the #2 or WW ingots to this block and it leaves no indentation on the block. Anybody got any ideas what I have here?