What type of rock is this?

[Curlymam88]

Does anyone know what type of rock this is please? I have a load in my garden as a stone feature. Located uk, wales

Like a pp, I thought it could be slag from blast furnaces especially if you’re in south Wales. When I was little there were garden walls built from it in my grandmothers street. There still is at least one locally. I’m also in the grey area on the map.

Used to buy this for our gas BBQs