Viren Agarwal was a coal-mining engineer in India in the 1960-1970s. Down in the mines he saw a piece of Indian sate and thought it would look good on a house. That one idea became a business exporting slate and sandstone to Europe and Australia — a way of looking at stone that three generations have kept: at the source, by hand, for quality, with an eye for how it will behave once it’s laid.