Since World War II the amount of information generated in the science of Gemology has increased tremendously. Therefore this book "Dictionary of Gems and Gemology" was written with the aim of providing a "relatively" complete dictionary to assist all students, hobbyists, scientists and interested parties in the fields of Gems and Gemology. The forerunner to this book was called "Dictionary of Gems and Gemology" (English-Persian, Persian-English, published in Tehran­ Iran in 1997). It was written with the aid of more than thirty refer­ ence books relating to gemology. In response to the effort required to clarify the terms within, I decided to compile a book that brings all the relevant terms into one book. This new book eliminates the use of different reference books and compiles nearly all the relevant terms into a one-stop useful text. It took twenty five years to collect the terms and the information so as to present a complete and functional lexicon. The text is supported by nearly 170 illustrations and 21 tables to provide detailed and succinct information. I hope and trust that this book will reach the high standard of other gemological dictionaries. If you have criticisms or suggestions, please feel free to contact me. Professor Dr. Mohsen Manutchehr-Danai Los Angeles, Tehran, Regensburg Acknowledgments The author acknowledges all those who were of valuable assistance during the writ­ ing and publishing of this book.