Author Topic: Weird Formation  (Read 525 times)

Offline pwhole

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Weird Formation
« on: August 07, 2020, 02:03:31 pm »
I photographed this strange thing a few years ago and it's always puzzled me what it is - does anyone have any ideas? Is it possibly a coral fossil?

Offline Andy Farrant

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Re: Weird Formation
« Reply #1 on: August 07, 2020, 02:52:54 pm »
Looks like load structures, or flute casts formed by erosive scour. They usually occur on the underside of a bed, and are usually formed by turbidity currents (underwater sediment slides). They are most common on the underside of sandstone beds deposited rapidly as part of a turbidite flow, although they can sometimes be formed by tidal scour. Is it sandstone?

Offline pwhole

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Re: Weird Formation
« Reply #2 on: August 07, 2020, 03:08:31 pm »
I was hoping you might know! No, it's in limestone - in Castleton, albeit not a bit regularly seen. It's in Pit Top Passage, high above the Bottomless Pit in Speedwell, which is mainly phreatic, developed on a fizzling-out vein - this is in one wall of the passage, and there's a tiny remnant of a vein just above it, so that may be a clue. It's the only occurrence up there (or anywhere that I've seen anyway), and seems to have been exposed by the miners. The colours are wonderful.

Offline rhychydwr1

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Re: Weird Formation
« Reply #3 on: August 07, 2020, 03:21:07 pm »
It looks a bit blue in the photo but if it is black and shiny I would suggest Galena or lead ore - PbS.

Offline moorebooks

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Re: Weird Formation
« Reply #4 on: August 07, 2020, 04:23:54 pm »
It looks a bit blue in the photo but if it is black and shiny I would suggest Galena or lead ore - PbS.

Could it be Blue John there?

Mike

Offline pwhole

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Re: Weird Formation
« Reply #5 on: August 07, 2020, 06:40:36 pm »
It's definitely as blue coloured as it is in the photo, and is definitely not galena - there's virtually none up there in that spot. Only the 'crust' is coloured blue or yellow. It's more of a formation that a mineral deposit as such - either limestone itself or a calcite deposition. It's the funny shape that gets me - it just looks very organic. I did see some pipe mineral that looked very much like Blue John in the Pit Props series but it didn't look much like this.

Online mikem

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Re: Weird Formation
« Reply #6 on: August 07, 2020, 07:00:02 pm »

Offline pwhole

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Re: Weird Formation
« Reply #7 on: August 07, 2020, 07:06:22 pm »
Ah! Now that looks closer, certainly. Thanks.

Offline AR

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Re: Weird Formation
« Reply #8 on: August 07, 2020, 09:37:50 pm »
I've seen blue crusts like that in a few other places Phil, my suspicion is that it's a hydrated iron phosphate.
Dirty old mines need love too....

 

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