Crumbs – rather inundated with comments about last Friday’s mystery object! Apologies for not answering all of the questions, the sudden leap in comments coincided with a particularly hectic day where I had virtually no computer access. The comments were wide ranging, from cannonballs to turtle eggs, truffles to coprolites (fossil dung), burnt cooking/toys to a bezoar. One of my favourites was the fossilised fist of a wood elf – and I can sort of see the similarity:

However, I am almost sad to say that it is none of the above. There were a few answers that came close, Don C suggested a concretion, Solius suggested mineral crystals, SmallCasserole identified that it was mineralised with a radial pattern, but one person had this hammered – Jeremy was spot on with with an identification of marcasite.

David Waterhouse from Norwich Castle Museum provided me with this description of the object:

this is a nodule of the mineral Marcasite (FeS2) closely related to Pyrite.  It was found on the ground in Thetford Forest about 20 years ago.  The whitish stuff you can see is chalk (marcasite sometimes forms from iron minerals within the Upper Chalk).  When fresh, this would have had a bright metallic lustre, but it has been exposed at the surface for many years and has dulled to the colour you see in the pictures.  Its orthorhombic crystal structure is difficult to see because of the weathering that has occurred.  It is heavy because of the iron in it, but not as heavy and less stable than pyrite.

So thanks to everyone who left comments – who knows, they may inspire future mystery objects. I’d better get looking for this week’s mystery object!