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Smooth spherical crystalline metal nodules

Smooth spherical crystalline metal nodules Outside and inside surface does not scratch with a knife blade Inside lustre brassy, radially striated metallic crystals radiating from a lumpy centre at the middle of the broken nodule are transparent crystals
Outside colour a dark reddish brown/black Found below the tide on the beach near Folkstone, UK

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    $\begingroup$ Kudos for adding a scale to the photo, but please read this guide and add as much additional information as you possibly can. $\endgroup$ – gerrit Apr 20 '17 at 13:11
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Your rocks are marcasite nodules. These nodules weather out of the chalk beds along the coast.

Here is a reference to UK chalk beds.

If you are interested, I would like to trade for one. I'll trade you a nice pyrite nodule I found here in northern Ohio near Lake Erie.

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    $\begingroup$ How do you know it is marcasite rather than pyrite? $\endgroup$ – bon Apr 20 '17 at 15:58
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    $\begingroup$ It could be marcasite or pyrite or both. Sedimentary environment would support either version FeS2. My field experience has been that marcasite nodules tend to be smoother modules than pyrite. Radial pattern on the interior of the nodule is also more commonly associated with marcasite. The center of the module might be pyrite. $\endgroup$ – Gary Kindel Apr 21 '17 at 12:10
  • $\begingroup$ Thanks for the identification. Having read the information on the link I would agree that the nodules are Marcasite. If I find any more then I would be willing to trade. The ones I have are remarkably tactile... $\endgroup$ – R. Spence Apr 21 '17 at 14:19
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They also come out of mesosiderites and my guess is the crystals are diamonds.

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