ACKNOWLEDGMENTS
I thank Dr. Carl Francis and Ray McDougall for offering suggestions toward improving this article. All of the photos are by Jeffrey Wolk except for , which is a Dr. Carl Francis photo.
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Notes on contributors
John S. White
John S. White is a consulting editor of Rocks & Minerals. Now retired, he is the former curator-in-charge of the National Mineral and Gem Collection of the Smithsonian Institution.