More than any other gem, each opal is distinctly an individual. No other stone has as rich and varied a folklore. Opals are also the most delicate gems commonly worn. They require special care to insure their health and longevity.
Opal's fire was long thought to be the result of iridescence. However, with the advent of scanning electron microscopes, we now know that it is a result of diffraction.
Opal is relatively soft, with a rating of 5.5-6.5 on the Mohs Scale. Despite its frequent use in rings, opal is a poor choice for a ring stone; it is much better suited to earrings, pins, and pendants.
Major suppliers include Australia, Brazil, Mexico, and the US. Values are normally determined by the presence and nature of color flashes.
An opal doublet consists of a slice of opal glued to a black backing, designed to imitate the appearance of a solid black opal. Adhering the slice of opal to a black backing causes the colour to become much darker and more vibrant. Opal doublets are highly regarded as an inexpensive alternative to solid opals which are very expensive in larger sizes.