Production 1978 - 1985 has averaged $25 000 000 per year. Mining is now mainly by mechanized methods in underground workings, most of the older shallower fields having been worked out. All areas of deeply weathered Bulldog Shale, or Russo Beds overlying Bulldog Shale are prospective for opal. However, the particular type of weathered profile found in known opal fields is a guide to more prospective areas within weathered Bulldog Shale. In places, fault type structures (`slides) may be a more localized control. Known opal fields occupy only a small part of the prospective area on the Precious Stones Field (PSF) and potential for finding new fields is high. Includes a description of individual fields in chronological order of establishment and miners and geological terms used in the opal industry.