Heavy black reconstituted stone? cylinder vase with white polka dots

I've had this a while and am no nearer knowing anything about it than the day I bought it, so any ideas at all will be extremely welcome, although I think this will be a tricky one!

It is a cylindrical and made from heavy stone. It's certainly not clay, so apologies if I'm posting in the wrong section, but I wasn't sure where to put it. Incised or carved out pot holes which have been painted white. No idea how this was made or indeed what it is made from (granite? marble? slate?). It appealed to me at the time because it had a Op Art look about it ( I'm a Bridget Riley fan!).
There is, I hesitate to call it a mark, some kind of shape on the base.

Height of about 9 inches and weighing over 1.6 kg.

Anyone have any thoughts on what its made from?

Looks like stoneware clay with loads of kaolin, feldspar, mica,& quartz

Thanks Dan.

looks like concrete to me