.....could it be Walnut?
Do you know what, Roger, I do believe you're right. When I first saw the piece it was still standing, but the trunk, from about a yard/metre high, had snapped off. What was left was about a foot diameter, perhaps a little less....this lump was a gall that had grown on the outside of the trunk, so I trimmed a piece off the trunk, shaped rather like a length of pipe, with this on one side. It was soaking wet when I cut it down, which would be about a year ago, and I had no idea what would be inside the gall.
I took a couple of cuts down the length of the pipe, threw the scraps onto the firewood pile and put the remaining piece, with the gall attached, into my turnings pile in the workshop.
Today I screwed through each of the 4 corners, onto a wooden faceplate and started skimming the outside of the gall...
...couldn't believe my luck when I saw how good the wood was and how well it machined.
In this next pic, the piece is now fixed into a chuck and you can see the remains of the rotten heartwood, which was bone dry when I cut it.
There was a limit to how thin I could take it, which became obvious when I stopped the lathe, checked out the inside of the gall and realised that it had been attached to the trunk by no more than an inch-wide strip of growth, which I had just started cutting into. One side is down to little more than a half inch left intact!.
In the next pic, it's reversed and held between a wooden dolly clad with router matting, and the tailstock live centre. A piece of the blue router matt is visible poking out of one of the holes.
Next I did a little more undercutting of the rim, but had to stop that when I realised how close I'd come to cutting it off the gall, so I settled for hand sanding it and cutting away the chuck tenon to form a little foot.
...and this is it, cleaned up and with a couple of coats of lemon oil. i decided not to build up a finish on it, as it will be impossible to buff safely.
...and here's that top-view again. You can clearly see the ring of bark between the outside of the trunk and the inner face of the gall, with the two small bridges of growth connecting the two pieces, at about 10 o'clock and 5 o'clock. Thank goodness I stopped cutting when I did!
Getting back to the species.....the heartwood has all the hallmarks of the beautiful swirls and the deep, purply-brown colour that can be found in walnut, and the bark was a silvery grey and quite deeply fissured, so I'm fairly confident that it is walnut.
C&C always welcome....Les