Sigmar Polke's stone windows

On my list of things to someday see are Sigmar Polke's agate windows at the Grossmünster in Zurich; in a 2008 New Yorker piece, Peter Schjeldahl wrote that Polke "conceives his stone windows as symbols of the creation, conjoining base matter and celestial light." Later, there's this bit, which I love: "This got him onto the subject of rounded forms in nature. He said, 'God made the earth in small circles.'" 

More images here + here.