Last time I was in Cwmorthin I found an unusual mineral deposit in a tunnel wall on lake level.
It consisted of a trace amount of candy pink powder, and the only likely match I can find in mineral ID books is with pink cobalt bloom.
We tried to take a photo, but it proved impossible due to the smallness of the deposit. Can't think how we actually came to notice it, as it was so very small an amount.
It was in a cross cut tunnel if I remember rightly, rather than in a chamber, so probably, given the location, in strata between the back and old veins .
Is cobalt a possibility in this kind of geology?
'I wonder how many breakfasts, and other meals we have missed inside that nasty clockless, timeless hole?'
'The Hobbit'
J R R Tolkien.