1. School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K.
2. School of Engineering, University of Newcastle, Newcastle upon Tyne, NE1 7RU, U.K.
3. Department of Physics, University of Warwick, Coventry, CV4 7AL, U.K.
4. Gemological Institute of America, 50 West 47th Street, New York, New York 10036, United States