Can anybody help identify this rock/mineral please? Found in Forest of Dean on an old railway track. Morphology like a piece of flint. The blue colour is fairly true to life. The blue feels like very hard plastic. I'm not convinced it is naturally occurring and may be a piece of slag or bi-product of an industrial process used as hard core on railway.
it looks to me to definatly be a chert nodule, the waxy feel of the 'hard plastic' and distinctive curves on the fracture are a give away.
flint, chert, chalcedony, quartz are all broardly the same stuff; silica dioxide. but the mineral can crystalise in many differing forms and including other trace minerals which effect the colour.
agates opals obsidian rose-quartz are all based on silica dioxide, and they have a huge range of colours and shapes.
i would hazard a guess that this could be classified as a "blue chalcedony"
hope that helps
What you have there is exactly what you have called it..."Blue Stone" (or as Jam rightly states blue chalcedony). It was quarried above and more frequently hunted for, on the beaches around Newhaven, one of a few known places where these Blue Stones can be found. They were sent to the local pumice factories to be ground up into powder and sold to the perfumeries to be used as face powder.
So it is naturally occuring and probably one that got away when flints were quarried and transported around the south coast and other areas of Britain where flint is not a natural deposit.
Certainly not native to Forest of Dean geology and Newhaven is a long way away...
I suspect it is either introduced by accident as part of the railway tracks (current sleepers are wide gauge from London, I was told by a man cleaning them when I was there last year) OR an artefact (slag-type)
Actually got my place wrong, it was Seaford head (even further away) that they hunted for these blue stones. Seaford wasn't the only place to get them apparently, but there was a huge industry transporting pebbles to all parts of the UK as aggregate and for building materials. The grey/blue stones (surface colour, black/grey inside), pebbles that were not trapped in sand/clay or chalk for millenia (which develop a brown or white complexion) were ground up and used for glaze in the pottery industry, but the Bue Chalcedony was highly prized in cosmetics for talc production amongst other things. Teams of hunters would pick out these stones and sell them to the warehouses up until the early 1920's and Seaford was one of those places that produced these stones on the beaches or were quarried fourther up the cliffs. I presume the close proximty of Seaford station circa 1850 helped with the national dispersal of flint.
http://chalcedonymine.com/blue-chalcedony-new (top grade stone)
I am assuming then that the stones that Ambler found were these, but not knowing the weight and texture could mean they are a bi product. Its been an interesting topic though.
The link is just a picture as an illustration of what the stone looks like, not a map reference point.
I have researched further and I was actually right about Newhaven though Seaford did have a small share in base flint export.
I have found 3 references that may point to this Blue Stone, which may be what the OP had found. I also think its worth noting the calcified exterior of the object, if this was indeed part of a smelting process it would be blackened or charred and the object would have a more uniform, analogous form throughout, like slag. and as far as I can determine, there is no industrial process (chemical) to produce hard core per se, apart from size selection from quarries i.e. the breaking up of boulders for different grade aggregate or mass collection from shingle deposits.
The third is of Rye and gives an example of trade costs etc.
In that 3rd link the author indicates areas of flint collection.... "Sources of flint were the Sussex coast, parts of Dorset, East Anglia and France" and Dorset is closer to FoD than Newhaven, so maybe the OP's find was one that came adrift from transportation to Staffs, who knows but its been an interesting piece of investigation.