Many books have been written about the gemstone, precious opal. With few exceptions, these have dealt with the subject in a popular manner, and all make enjoyable reading. Why do we need another treatise on the subject?

There are many forms of opal; the gemstone is only a very special and rare variety of the mineral as it occurs in nature. Even common opal is a fascinating study, because it occurs in a wide variety of forms, many of which can be used to produce attractive ornaments. In addition, there are those forms which come under the general term of "opaline silica", many of which are important industrially. The aim of the disc is to bring together the history and mythology, the occurrence and production, the stories of the "opal people", the properties and science of opal, as well as its uses and some potential dangers.

It is hoped that there will be enjoyable reading and browsing for the general reader, as well as being a source of technical material for professional in mineralogy, gemmology and related fields. Included, therefore, are outlines of both older and more recent scientific studies on opaline silica of all types. In addition, the bibliography should lead directly to amplified information in all fields.