In compiling the material for this disc, I owe much to many people who have helped me during my work on this fascinating material. First and foremost, I am indebted to my friend and colleague, Dr. J. B. Jones, of The University of Adelaide, with whom I collaborated for 15-20 years, resulting in the publication of numerous formal papers and articles on opal and opaline silica. During this time, Dr. C.A. Anderson (formerly from the CSIRO Division of Wool Research, Geelong, Victoria) produced a wealth of masterly scanning electron micrographs, and Dr. J.V. Sanders carried out the original transmission electron microscopy on our materials, including the first sample of precious opal examined, producing many remarkable results.

Mr Andrew Cody has been most generous in allowing us to use sections from his book, "Australian Precious Opal", and in supplying many photographs. Many people have helped in many ways, and I am most grateful to Dr. John Webb (Latrobe University), Dr. Bill Birch (Museum of Victoria), Mr Len Cram (Lightning Ridge), Mr Peter Hynes (of Ballarat), and Mr T Lindner (Coober Pedy), who supplied numerous illustrations.

Special thanks are due to Mr Michael Todd for editing the final text, and to the Mines Departments of the opal-producing States for permission to use some of their published material

And finally, but not least, I owe much of the arrangement of this material onto the various databases, as well as the formatting of many of the diagrams to my son, Carl Segnit, without whose help production would have been much more difficult.