http://www.bbc.co.uk/news/uk-wales-29250105 

It is actually a slate mine.

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Yes- it's the old Coed-y-Glyn slate mine and quarry. Oh, if I had the money, but I suspect even then SWMBO wouldn't let me..... ;(;(;(

Grahami

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It's granite, not Slate.

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Hi Newstuff,
Have a look at :

http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/viewer.html 

I'm afraid there's no granite round there, some igneous intrusions, but no granite.

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EDIT:- Totally re-written, as constant editing made it sound snarky, which it wasn't meant to.

I'm not too sure on how to read that overlay, but I'm pretty sure it's a granite mine (Arguing with a geologist, famous last words eh?).

That rock I PM'd you a picture of came from here, and the abandonment plan has "Coed y Glyn Granite Quarries" as it's title. PM me for a copy, the cross section lists green granite and brown granite mixed with lava (possiby what that rock I sent you a picture of was... maybe?)

There's also Upper Pandy and Hendre around here listed as Granite (all served by the Glyn Valley Tramway). You know better than I do, but maybe it's not been entered properly on that overlay?

http://en.wikipedia.org/wiki/Glyn_Valley_Tramway 

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Wales is not noted for Granite, or even granite type rocks.
It presumably is some sort of igneous or metamorphic rock which can be pretty hard, and so marketed as 'granite'
All granites contain three distinct minerals:
White quartz, may be brownish if iron stained.
Feldspar, again usually white, though pink and red varieties occur.
Mica usually present as black spots in the rock.
I suggest you look at your rock samples andd see if it fits into the above.

I hardly think that the local "granite" was called this because of it's mineral composition. It will have been called "granite" simply because it is hard and heavy, as John says. Stonesfield slates are not slate. I think some of the cherty deposits in parts of Surrey were locally referred to as "granite" which they very clearly are not.

I'm not a geologist. I'll see if I can find aforementioned rock, and give it to rockchick next time I see her. I have a feeling the daughter took a liking to it, so it's anyone's guess where it is now.

EDIT:-
A picture of the rock can be viewed here.

https://www.flickr.com/photos/new_stuff/6280049721/sizes/l/in/photostream/ 

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I thought the setts used for paving half the UK's city streets came down that valley ... that may be a slight exaggeration.

OK - I sit corrected, it's not slate, - so what was being mined then ? I'm sure there was something in my old copy of the GVT, wasn't silica was it ??

Grahami

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I'm not sure what was being extracted, but there is a Silica mine in that area (Pen-y-Graig).

A link to the abandonment plan. Be warned, it's huge. 27MB and 11693x9802 pixels. Slow/old computers may well choke on it.

http://www.4shared.com/download/f5IT6ufdce/Coed-Y-Glyn_-_Original.jpg?lgfp=3000 

Rockchick may like the cross-section (on the right hand side).

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Many thanks for that - intriguing plan.

Grahami

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Peter, as you stated, bit of exaggeration that most of the paving setts came from there!
The ones for most of the Northern Towns(west coast), came from my area, here Dumfries & Galloway, which shipped granite setts down to Liverpool

Granite setts for the east coast came from the area of the Granite city, Aberdeen and again off loaded in London.
Paradoxically because of the virtual closure of theses Scottish Quarries, recent sett replacements, have used Chinese granite!.

There is so much solid infrastructure still around and rarely does anyone think about where it came from. A bit like food.

A neighbouring grade 2 listed cottage had to use South African stone slate to re-roof, the best acceptable match to suit the National Park!.

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I was more making the point that things like street cobbles, wall coping stones, etc etc all had to be carved out of the ground by hard-working men in the back of beyond, and now they are just part of the town landscape, as if they have been there forever.

Hi Newstuff,
If it was a granite i'd expect to see largish (2-5mm) white hard crystals (quartz), micca (shiney black crystals) as well as feldspar (pink or white) there doesn't seem to be anything like that, so i'd rule it out as a granite.

Looking at the geological map for the area, it's mostly mudstone, siltstone and some smallish igneous intrusions and tuff.

One unit is identifed as:
Pen-y-graig Tuff Member - Volcaniclastic Rocks (both Pyroclastic & Reworked Volcanic Rocks). Sedimentary And Igneous Bedrock formed approximately 455 to 456 million years ago in the Ordovician Period. Local environment previously dominated by explosive eruptions of silica-rich magma. I suspect this is what your photo's of.

It's interesting that plan identifies granite on it, i suspect that may relate to early geologists/surveyors who as discussed were just identifying rock with slightly generic terms. The 'lava' identified on your plan will probably be the igneous intrusions in the area.
Hope that helps.

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Having been there and looked at other mines in the area, it is all slate. 😉

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rhychydwr - Although many others in the area are slate(it's my local stomping ground) I can assure you, this one is not slate. 100% guaranteed. I have been in it. Have a look at the picture of the rock I linked above.

Rockchick - If I can find the rock in Question, I can do Macro's down to an insane level.

Grahami - No problem. It's a lovely scan of the map for an interesting place.

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Thanks Newstuff, but it would be much better to just have a look at the rock next time I see you! :thumbup:

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