Originally Posted by
Iceni
Looks like a slate type to me.
The UK has a lot of places that produce decent slates for hones. There was a big slate industry running from Wales and Cornwall. This doesn't mean that the stone actually came from the UK. The problem with standard coloured slates is they appear in lots of places worldwide. And without identification marks like colour and inclusions you have no chance to even guess the origin.
Slates also have huge differences in the final finish. So you will only know by using it and comparing it to a modern synthetic if it is a razor grade finishing stone. The vast majority of slates I have come in somewhere between 3 and 6K. You can finish on them but the shave from the rock is pretty rough. Using pastes after the slate can fix that. I find it acceptable in most cases for knives and tools. Modern synthetics like the Naniwa 12K have eclipsed slates both in speed and finish. Oil makes the finish better, but it also makes them slower.