Another Thing To Identify Please

[The Old Ruminator]

No its not a potato. Buried in sediment inside a cave. Andy F. will know.

P8110003 by Nicholas Chipchase, on Flickr

[Alex]

A poodle?

[traff]

Ginger root?

Sorry not helping.....

[Roger W]

Ironstone nodule???

[mikem]

Toy from mother shiptons

[Brains]

Chert nodule

[Pete K]

I'd say chert too. Chip a bit off if you can bear to and see if it looks like a poor man's flint inside. Giving it a really good clean and maybe a sand down might reveal what's inside less destructively.

[Andy Farrant]

It is most probably  a chert nodule. If it is from East Mendip, you do get chert nodules in the limestone (particularly common in the upper part of the Black Rock Limestone), but as ever it is hard to tell from a photo, especially when caked in mud. The other possibility is an oncolite (an algal concretion akin to stromatolites) which do occur in the Clifton Down Limestone, but the morphology doesn't look right. Best to clean it and if it is very hard and siliceous, then it is chert.

[The Old Ruminator]

Thanks all. It came from Bleadon Cavern, West Mendip.

[The Old Ruminator]

A bit more from the finder.

It came from a filled mine shaft on Bleadon Hill in ocherous  earth. It has been cleaned, a smaller similar one is CaCO3  - massive fizzing with HCl - and grey inside, not chert. I have a similar piece that has formed as a crust rather than a nodule. Don't want to break the poodle, but will hopefully find more tomorrow.

[Pitlamp]

My attention's just been drawn to this by a friend; can I ask, is your specimen at all granular inside?

By this I mean could it be a calcite cemented sandstone?
(Or even calcite with some SiO2 [sand or silt] grains within it?)
Both would react well with HCl.

I ask because we found something similar in a cave in the Dales this summer. Just wondering if we could learn anything useful from you, if you've investigated further since the last post around three months ago. Thanks.

[Pitlamp]

In fact - any chance you could post one of your excellent photos of the cleaned up "poodle"?

[Pitlamp]

Here's the one I was on about in my post above. It came out of a sump which now carries only percolation flow and the hemispherical blobs are composed of calcite cemented sandstone on the surface of the limestone block (i.e. they're not inclusions within the limestone itself). There are several other examples still in the sump in question.

Samples of these blobs have been sent to people who know a lot more about this sort of thing than I do but no consensus as to their origin has yet been arrived at. I'm told that no such thing is included in Art Palmer's book on cave minerals of the world (with thanks to the person who looked on my behalf).

Just wondering if any forum users might have useful suggestions - and whether there's any connection between these blobs and the item brought to our attention by The Old Ruminator above?

[mrodoc]

I would have said this is a concretion as you surmise. Reminds me of the Moeraki boulders in New Zealand's South Island on a miniature scale. There are papers on the origins of the Moeraki boulders that might help hint at the origin of your concretion.

[Pitlamp]

Thanks mrodoc.

Meanwhile, here's another example with the limestone broken, revealing that the blob is on the surface rather than within the limestone.

[Pitlamp]

Following up mrodoc's suggestion:

https://www.distantjourneys.co.uk/blog/moeraki-boulders-natural-phenomenon-mysterious-legend/

Interesting - there may well be clues here.

[mrodoc]

Might as well stick a pic  in of a Moeraki boulder just for the hell of it.

[grahams]

It appears to be a Slipperman.

[mikem]

Formation of nodules within the rock:
https://www.open.edu/openlearn/science-maths-technology/science/geology/fossil-bonanzas

Useful guide to identifying minerals etc:
https://www.clemson.edu/public/geomuseum/specimen_id/id_tool.html