Wow thanks everyone it does seems as though I found a very interesting little lump of carcinogen! I hadn't ever imagined it would be asbestos. I hadn't even realised asbestos was something you'd find out in nature I always presumed it was like fibreglass and made made.
I've really enjoyed hearing about it's previous uses in the jewellery trade. I knew of it's use in soldering mats but had no idea it was used in other ways.
I'm a bit disappointed I didn't keep it now. I didn't think I'd be able to transport it without damaging it so I left it.
Thanks again everyone.