Looks like a piece of deformed laminated ferruginous mudstone.
It is not uncommon for relatively finely-laminated mudstone to be caught-up in folding events (at various scales including small, as here).
Some info on locality would be useful to help confirm that, as superficially there are also similarities to concretions.
Saddleworth - yes - that's the key!
Refer here and you'll see there is a John Buckley, who was an ironstone miner born in Saddleworth and living in Rosedale in the late 19th Century
Then refer here and you'll find mention of the Rosedale magnetic ironstone!
And for a fascinating account of the abandoned community of Rosedale, and the ironstone mining, have a read of this - http://www.abandonedcommunities.co.uk/rosedale.html
It is a great piece of research by Stephen Fisk. Lots of snippets of interest, eg. "In 1873 the Rosedale mines produced over half a million tons of ironstone. That was the most successful year in its history."
Now, to be honest, I can't strictly say that your specimen is from the same source, but it does seem highly likely.
Thanks for the question, Danny!