The amount of information generated in the science of mineralogy has increased tremendously since the mid-1970s when the first edition of the Encyclopedia of Min­ erals was published. This growth was enhanced by technological advances in analyti­ cal equipment and increased computerization. Combined, these have led to ad­ vances in structural determinations, phase equilibria, high-resolution microscopy, better quantitative analyses, and improved data processing, to name just a few areas. Ingenious microanalytical techniques have also been developed for mineral species whose abundance is measured in milligrams or less. Professional and ama­ teur mineralogists have become increasingly alert to the occurrence of potentially new species. The purpose of this book, as in the first edition, is to serve as a useful desk reference for mineralogical data. More than 400 species have been added to this edition, and data for many of the existing species given in the first edition have been revised based on new information. Changes were also made in the format, in hopes of making it more readable. Reflected-light data were added for opaque minerals, and new locality information is given for previously existing species. Although Bill Roberts left us much too early, we hope that this book will, at least in part, meet his exacting standards. Bill's spirit is preserved in the enthusiasm with which this edition was prepared.