An opal might display a single color, two or three colors, or all the colors of the rainbow. Opal displays background color in addition to play-of-color. Background color—also called bodycolor—is caused by the suspension of tiny impurities within opal’s silica spheres.

Opal is known for its unique display of flashing rainbow colors called play-of-color. There are two broad classes of opal: precious and common. Precious opal displays play-of-color, common opal does not.

Figure 1. Play-of-color is the defining characteristic of gem opals. While play-of-color can be quite spectacular under magnification, as with the roiled green patterns seen in this crystal opal, other microscopic features are often found if one takes the time to look. Field of view 9.60 mm. Photomicrograph by Nathan Renfro.

There are three main aspects of an opal’s quality. Color refers to background color and play-of-color. Pattern is arrangement of play-of-color. Clarity means transparency and quantity of inclusions. Play-of-color might be the most spectacular aspect of an opal’s appearance.

While play-of-color patterns can be extraordinarily beautiful under magnification, opals often contain a vast array of spectacular microscopic features in addition to this phenomenon. In continuing G&G’s series on inclusions, this chart will focus on …

Opal and tourmaline are the two birthstones for October. Both of these gemstones are known for their endless color combinations. Learn more about these two birthstones for October and discover their meanings and where they can be found.

Opal is the product of seasonal rains that drenched dry ground in regions such as Australia’s semi-desert “Outback.” It is known for its unique display of flashing rainbow colors.

Opal and tourmaline are the two birthstones for October. Both of these gemstones are known for their endless color combinations and are believed to have been created from rainbows. Learn more about these two birthstones for October and discover their …

Sep 19, 2011 · The relatively new source for precious opal located in Ethiopia’s Wollo Province produces material with vibrant play-of-color and occasionally with interesting inclusions.

Opal’s microscopic arrays of stacked silica spheres diffract light into a blaze of flashing colors. An opal’s color range and pattern help determine its value. More About this Gem Buyer's Guide