Thanks ThomasPowers!
It's a Campo Meteorite which is an iron meteorite with about 6.7% Ni and a little Co and P according to published data. I also had a lab test it and their numbers matched almost exactly with that (7.0% Ni, 0.48% Co, 0.16% P, and 0.13% Si). I had it tested after forging so I think I forged out some of the Phosphorus because that number was lower than the published amount.
It's good to hear it can be used as a flux (but maybe not the greatest flux). I had accidentally welded it when I put the two bars together to get them flat before welding. I put them on my hydraulic press and pushed them together at what I thought was a temperature slightly lower than welding temperature. When I pressed it I could see the molten material get squeezed out, but then I couldn't get the bars separated, even after reheating and banging them around. So I've been worried that the weld isn't good quality because there might be a layer of impurities. I'd like to think my weld is good and I have no reason to think otherwise, other than I've never tried a weld like that and I was question my work.
Thanks again - it's great to have a resource like this with experts in the craft!
James