It seemed like an odd choice to me at first, but they probably chose calcium carbonate because of its ability to polarize light: http://www.daviddarling.info/e

It seemed like an odd choice to me at first, but they probably chose calcium carbonate because of its ability to polarize light: http://www.daviddarling.info/encyclopedia/P/polarization.html http://www.daviddarling.info/encyclopedia/P/polarization.htm...