This book contains a wealth of information on various types of opals, their appearance, diagnostic properties, imitations and how to tell the difference between potch and precious opal. Designed for the beginner or experienced, it will greatly assist those wishing to find out more about how to correctly identify opals. There is also details on the correct readings for opals, from various gemmological instruments, such as spectroscope, polariscope, refractometer, and more, which will aid in accurate identification. This is book 9 in 'The Australian Gemstones' Series.