The chimney was built 1857-1858 and once had an associated engine-house and arsenic calciner. Yes, it was yet another part of the burgeoning arsenic industry. It's a particularly decorative example, as at the insistance of the Duchy of Cornwall, who apparently felt that if you were going to stick a giant chimney on a prominent hill to burn poison, it was really important that it was built in the form of a monumental column.
The mine underneath, which must have hollowed out a great deal of the hill, was mostly a tin-mine. The North Engine shaft was 110 fathoms deep - that's 201 meters. Having bored you with my photos of the outside, let me now link you to some rather more interesting photos of the inside.
Nowadays the chimney comes in handy as a place to stick mobile phone masts.
I've just discovered that the rather grandiose chimney was constructed on top of 'two concentric stone revetments built upon a mound' which probably supported a windmill.
Suddenly I feel that the mere chimney is rather understated. A windmill on top of this hill must have looked amazing! All the trees around it are short and stunted and growing tucked away into folds of the ground though, so they must have had to be awfully careful with the sails when the wild winds blew in from Bodmin Moor or Dartmoor.