Opal is the most colorful of all gems and possesses a fascinating structure. As this structure is not truly crystalline however, the gem is actually considered a mineraloid, and is made of hardened silica gel. The play of colors witnessed in Precious opals means it is said that in them you can see all of nature’s splendor, including flashes of fire and lightning, rainbows and seas.

Opals can range immensely in color, with green and white the most common, and red and black the rarest and some of the most valuable (though ‘black’ opals not actually black, simply darker in hue than other shades of opal). Due to the refractive nature of the gem
Opals can range immensely in color, with green and white the most common, and red and black the rarest and some of the most valuable (though ‘black’ opals not actually black, simply darker in hue than other shades of opal). Due to the refractive nature of the gem

Background and Types of Opal

Around 95% of opals come from dry and remote desert areas, and the gem has long associations with Australian Aborigines and the Outback. With this in mind it is perhaps unsurprising that it is the national gem of Australia, with the vast majority of the world’s opal production coming from Australian sources such as the towns of Coober Pedy and Lightning Ridge. Outside of Australia, other significant deposits have been found in Brazil, Turkey, Hungary, Indonesia and Honduras. Opal has even been discovered on Mars.

Left:  An Example of Fire Opal

Opals can range immensely in color, with green and white the most common, and red and black the rarest and some of the most valuable (though ‘black’ opals not actually black, simply darker in hue than other shades of opal). Due to the refractive nature of the gem, however, flashes of any color of the rainbow are possible. Opals contain a small percentage of water, meaning they should not be stored in dry heats for long periods of time otherwise they may dry out and crack. The humidity they require from the air makes them excellent for items of jewelry.

A number of gemstones make up the category of Precious opals, all of which shine and sparkle, with a continually changing play of colors. These include Black opal, White opal and Precious Fire opal. Opals that lack this play of colors are known as Common opals. The gem has a hardness rating of 5.5 to 6.0 on the Mohs scale.

Factors That Affect Value & Treatments

The main factors that affect gemstone valuation are the ‘Four C’s’ of color, cut, clarity and carat (size), as well as geographical origin.

The distribution and intensity of its color flashes help determine the value of an opal. The rarest colors such as black naturally command the biggest prices, and the highest quality specimens can match even diamonds, rubies and emeralds in value. Common opals lack the ‘play of light’ effect and do not command high prices, though gemstones are still cut from these forms of the stone.

Synthetic opals also command a small share of the market, and are distinguished from natural specimens under magnification. Many synthetic opals are made in Japan.

Opal Meanings and Properties

Like many gemstones, opal had many meanings and properties in the Middle Ages, when it was believed to bring luck. It is also said that the color play of the gem reflects the changing moods and feelings of humans, with opals believed to possess considerable healing powers, encourage faithfulness and loyalty, eliminate depression and help the wearer discover love. Opal is also the birthstone for the month of October.