An exotic type of greenstone has been worked at Polyphant, near Launceston, where it has been quarried since Norman times. The Polyphant stone is quite soft, but is a superb medium for carving and will take a lustrous polish, producing a dark- green shiny surface. Many churches in east Cornwall and further afield (including Canterbury and Exeter Cathedrals) have interior features made of Polyphant stone. I think the quarry is still used for a few weeks a year.