Exposures of in situ minerals in mines are just as natural as calcite growths in caves, expect that man has dug a mine to expose them. There are numerous protected sites around the UK called RIGS which I think means Regionally Important Geological Sites, many of which are artificial exposures of geologically important features. The English Nature website might have information about these. There are probably similar SSSIs. The minerals in a mine are usually (but not always) the reason why the mine was dug in the first place. Damage to good mineral exposures is removing part of the story of the site. I would only condone removal of minerals from piles of mine waste, and there are probably some who would frown at this too.
Since it's illegal to take stalactites from caves in this country, if anyone purchases them, would they be liable for prosecution because they'd be in receipt of stolen property? Or would that only apply to stals taken from British caves?Gus
I don't think that the seller will take any notice as all he sells on E-bay is minerals, fossils and cave formations!!!!