Cornelis ('Kase') Klein is Emeritus Professor in the Department of Earth and Planetary Sciences at the University of New Mexico, Albuquerque. He received his BSc and MSc in geology from McGill University, Canada, and his PhD from Harvard University, Massachusetts, also in geology. He has been a member of the geology faculty at Harvard University, Indiana University, Bloomington, and the University of New Mexico, and has taught courses in mineralogy at all these universities. His published books include Manual of Mineralogy (19th-21st editions), Manual of Mineral Science (22nd-23rd editions) and Minerals and Rocks: Exercises in Crystal and Mineral Chemistry, Crystallography, X-Ray Powder Diffraction, Mineral and Rock Identification, and Ore Mineralogy, 3rd edition (2007). He has received two awards for excellence in teaching from the University of New Mexico. Anthony R. Philpotts is Emeritus Professor of Geology and Geophysics at the University of Connecticut, a Visiting Fellow in the Department of Geology and Geophysics at Yale University, Connecticut and Adjunct Professor in the Department of Geosciences at the University of Massachusetts. He received his BSc and MSc in geology from McGill University, Canada, and his PhD from the University of Cambridge. He has taught igneous and metamorphic petrology courses at McGill University and the University of Connecticut for more than forty years. His published books include Principles of Igneous and Metamorphic Petrology, 2nd edition (Cambridge, 2009) and Petrography of Igneous and Metamorphic Rocks (1989, 2003).