Hi This is almost certainly the famous marcasite vugh!
To those of you who are not aware, Marcasite is similar in Chemical formulae to the more we’ll known Iron Pyrites.
The main difference being marcasite is not very stable and in damp air will rot to nothing!
Hence the interest at the time and the collecting foray!
Under certain circumstances Marcasite can even be pyrophoric, ie it will burn when it meets the air. Tara Mine in Ireland had some problems with this mineral, of this nature. As far as I am aware this catching fire never happened at Grove Rake....replace this line with your message...
Photograph:
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