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Can you identify this 'hedgehog'?
  
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Steve Cole




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PostPosted: Aug 18, 2017 14:21    Post subject: Can you identify this 'hedgehog'?  

Found on the 'South Downs' in Southern England, this is very different to the usual chalk and flint in that area. It is 5cm across, rather heavy, not influenced by a magnet, and covered in triangular crystals. It cannot be easily scratched by a pocket knife.


Mystery Rock.JPG
 Locality:
Fulking, Mid Sussex District, West Sussex, United Kingdom England
 Dimensions: 5cm
 Description:
Fulking Down, West Sussex
Compared with a UK £1 coin.
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kushmeja




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PostPosted: Aug 18, 2017 14:37    Post subject: Re: Can you identify this 'hedgehog'?  

Based on it's appearance and the minerals in that area, I'd say that it's pyrite that was partially altered to limonite. Mindat has pics of a pyrite nodule in flint that was found in West Sussex that looks very similar, but not altered to limonite.
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Peter Megaw
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PostPosted: Aug 18, 2017 14:39    Post subject: Re: Can you identify this 'hedgehog'?  

Looks like a partially oxidized marcasite nodule from a sedimentary formation. It probably smell sulfurous if you take a whiff.

It will almost certainly continue oxidizing and eventually fall apart. You might be able to slow that down by washing with 90% isopropyl alcohol to kill the bacteria that hasten the oxidation. Scrubbing with a toothbrush to remove the rusty oxidation may reveal some of the golden metallic color of the marcasite.

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Joseph DOliveira




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PostPosted: Aug 18, 2017 15:26    Post subject: Re: Can you identify this 'hedgehog'?  

I'm with Peter on marcasite, very similar to the marcasite nodules from the Belle Fourche Reservoir in South Dakota. If you're looking to clean them up and remove the oxidation, a light blasting with a sand blaster and glass beads will do nicely.


Peter Megaw wrote:
Looks like a partially oxidized marcasite nodule from a sedimentary formation. It probably smell sulfurous if you take a whiff.

It will almost certainly continue oxidizing and eventually fall apart. You might be able to slow that down by washing with 90% isopropyl alcohol to kill the bacteria that hasten the oxidation. Scrubbing with a toothbrush to remove the rusty oxidation may reveal some of the golden metallic color of the marcasite.

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Steve Cole




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PostPosted: Aug 18, 2017 16:29    Post subject: Re: Can you identify this 'hedgehog'?  

kushmeja wrote:
Based on it's appearance and the minerals in that area, I'd say that it's pyrite that was partially altered to limonite. Mindat has pics of a pyrite nodule in flint that was found in West Sussex that looks very similar, but not altered to limonite.




Are you able to give me a link to the Mindat pictures? Thanks!
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Roger Warin




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PostPosted: Aug 18, 2017 22:32    Post subject: Re: Can you identify this 'hedgehog'?  

Hi,
Yes, a marcasite nodule. Radiating crystals.
These concretions are frequent in the north of France in farming areas. Dimensions up to 15 cm in diameter
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