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Visit to the Blue John sites in Derbyshire, UK
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PostPosted: Nov 11, 2008 13:20    Post subject: Visit to the Blue John sites in Derbyshire, UK  

Hi everyone,
I’m new to the forum, so first a brief introduction. I live in the UK, close to Heathrow Airport. I was interested in geology from around age 10 and went on to study it to first year level at university (before dropping it in favour of botany. Maybe a mistake!). I started a small mineral collection in my twenties but after a while life’s complexities took me away from this for many years. Now in my fifties I am reviving my interest and starting to collect again. I have a particular interest in collecting the minerals from the famous Florence mine, Egremont, Cumbria, U.K., sparked by a visit there over 30 years ago. Other than this I have decided in my “re-awakening” to collect anything from anywhere that I find aesthetically pleasing.

Amongst other mineral delights, Derbyshire in the UK is famous for the ‘Blue John’ variety of fluorite. I recently visited the Blue John caverns and Treak Cliff cavern, the two sites containing the mineral. Sadly I didn’t have my camera as it was an unplanned and unexpected visit but I do at least have photos I can share of the specimens I returned with.

The caverns are open to the public all year round and can only be accessed via guided tours. I was most fortunate in arriving early on a cold, miserable morning just as they opened for the day. Why fortunate? Well, one of the guides explained that for health & safety reasons they normally do not do tours unless there is a minimum of two people plus the guide. But he said as it was unlikely anyone else would turn up for a while, he would take me down on my own and give me a personalised tour! Because it was just the two of us we could chat away and he soon realised that I was actually interested in the geology and was not a mere ‘tourist’. He explained that the guides are also the miners, working at extracting the Blue John during the quieter winter months. I have always loved caves and the caverns here are classic limestone types with all the stalactites, stalagmites, flow stone and the like that you would expect in such systems, as well as the mineral occurrences.

Due to my interest and being on our own, my guide took me off the usual tourist route and showed me where they were currently extracting the Blue John. They have been mining it here for over 300 years. All the best quality seams and particularly the larger ones have long since been exhausted. What is left occurs as fairly narrow seams along the bedding planes of the limestone, with occasional larger pockets. He explained their mining method – small holes are drilled all around the seam or pocket they want to extract. Lengths of wood are pushed into the holes and left for a while. The wood absorbs water (which is seeping down most of the walls in the mine) and expands, exerting pressure. A few well chosen taps with a hammer then causes the seam or pocket to pop out of the wall in a single piece. He showed me some of the recently mined Blue John and very kindly gave me a few small specimens for my collection (see photo below for one example). He said that the total amount they now mine each year is only about half a tonne, which goes almost entirely to local craftsmen for working into jewellery and other ornamental items as well as providing natural specimens for sale via the onsite gift shops. In its natural state Blue John easily fractures into small pieces so all of it has to be treated before it can be worked. This process involves injecting resin to stabilise the material so it can then be cut and worked without breaking into pieces. Because of this, each piece takes at least a week to produce. Prices of finished items are therefore not cheap, especially the larger pieces. Given that large pieces of Blue John are no longer found, the largest items they can make now from a single piece would be say a bowl of about 15cm diameter. These sell for around £550 (roughly US $1000 but currently exchange rates are dropping wildly!)

As well as the small representative samples given me by the kind miner, I bought a nice natural specimen showing some rough cubic forms (picture below). Blue John doesn’t often form defined cubes so the few specimens that do are much sought after. I also treated myself and bought a really fine cut and polished slice showing the banding the mineral is famed for (see picture below). So little material good enough to make such slices is now being found that the opportunity to buy such material will surely become increasingly rare.

Moving on to Treak cliff cavern, there were now a lot more tourists around and I only had a standard group tour. The difference between this and the personal tour was marked! – the young man showing us round rattled off his speal at top speed and seemed concerned only to get us through the place as quickly as possible. Despite this, it was well worth seeing – there is actually a lot more Blue John visible here than in the Blue John caves. Some very impressive seams have been left untouched, in some cases so the public can see what it was like in the days when such seams were common, and in one case a pillar of solid Blue John left because without it the roof would have collapsed! Particularly memorable in this area was a pocket in the roof where a rich area of blue john had perched on it several extremely large and fine dogtooth calcite crystals.

My visit was most enjoyable. Next time I’ll take a camera!

Blue John slice 640 x 480.jpg
Blue John cut and polished slice
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Blue John slice 640 x 480.jpg

Blue John 640 x 480.jpg
Blue John with some cubic form
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Blue John 640 x 480.jpg

Blue John rough 640 x 480.jpg
Representative Blue John given me by the miner
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Blue John rough 640 x 480.jpg

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Jordi Fabre
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PostPosted: Nov 11, 2008 13:57    Post subject: Re: Visit to the Blue John sites in Derbyshire, UK  

Hi Massonia, welcome here!

Very nice column. Thanks to share it with us.

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