One of the world’s rarest gems, the Blue Moon Diamond, will be on exhibit at the Natural History Museum of Los Angeles County from September 13 through January 6, 2015. The rough stone was originally sourced from the famous Cullinan mine in northeastern South Africa in January of this year. It was purchased by Cora International, a New York City manufacturer of diamond jewelry and a diamond supplier, for $26 million. Over the years, the Cullinan mine has produced numerous notable gems, including the largest-ev…