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From that test is hard to say as it was not done by clear copper as coim coppers are usualy made of alloy which makes them more durable. Normaly copper wire will scratch most of the slates but not CF.

Can you try to scratch the stone with clean copper wire? Does it gouges the stone or not. What is the size of the stone?

Yes I was in Whittle Hill quarry a few weeks back as I am trying to colate practical information about different sources of CF. I can not imagine that there were too many hones comming from this...