OPAL
There is one gemstone that has the ability to capture ancient rainwater and then use that water to create a rainbow with eternal life. That gemstone is called opal. Opal is formed when heavy rains pour onto the sandy plains of a hot desert landscape. The water carries some of the fine sands, called silicates, down into deep cracks in the normally dry earth’s crust. This water and sand get trapped in these open areas of the subterranean rocks. As the dry season returns, the ground is heated, and much of the rainwater evaporates. Over time this compacted silicate mixture hardens to form a hard crystal filling in the cracks. Some of the original rainwater is sealed inside these crystals as the outer edges form. A typical opal is usually between 6 and 12% water by weight. Once the stones are removed from the earth and polished the semitransparent stones let light into them. The light is then separated into its different color bands as it passes through these trapped water droplets. Just as when sunlight passes through falling rain, to create a rainbow, the same prism effect is happening inside this amazing gemstone.
The purity of the silicates, the concentration of water, and the arrangement of the microscopic silicates all contribute to the amount of color each stone can produce. There are essentially four different types of opal: white opal, black opal, boulder opal, and fire opal. White opal is the most commonly occurring variety of opal. It is a stone that has a milky white body color and has little flashes or spots of color that are encapsulated in the stone. The number of colors, the quantity of color flashes, and the intensity of saturation of these colors all determine the gem’s value. The “color play,” which is what the color flashes are called, can present themselves in two different fashions. The first, called pinfire, is where the colors show as little individual dots of color. Almost like glitter or confetti. If the colors are in sheets that move like a hologram below the surface, this is called harlequin fire.
Both of these are beautiful and each stone is of equal value. In other words; it isn’t how the color shows itself, it is the amount, quality of saturation that matter. The finest white based opals will display a full five color spectrum: green, blue, red, yellow and orange. The depth of these colors then come into play. As the internal color play becomes more present, the white base of the opal gets overshadowed. The more intense, or fiery the colors, the rarer the stone. In general, reds and oranges are the hardest color for the gem to produce. The more of these colors, the more rare and valuable the stone. Opal size and color consistency also help determine value. Any gem over 5 carats that has five color play and firey intensity is considered a fine specimen. This white based opal can also have the body color lean more grey or yellow, both of these are rarer and more desired. The white base opal is October’s birthstone and the gem most people think of when they think of opal.
The next type of opal, the black opal, is the rarest and most collectible of all varieties. Black opal occurs when a blackened layer of opaque dark opal form naturally either behind or within a white-based opal. The overall body becomes very dark, black or dark grey color. The black opaque opal that gives the black opal its color is called Potch. The same characteristics of quality apply to black opal. The fuller the color spectrum, the more saturated the colors, and the intensity of fire in a black opal can send the value of this rarity through the roof. A fine gem black opal with five color intense fires in 5-7 carats can go well over $100,000 for the stone. Most are held in private collections or displayed under glass in a museum. In comparison, that 5-7 carat fine gem as a white base opal could be $3,000-$5,000. (A grey based similar stone would commercially sell for $10,000-$15,000).
The third type of opal that is also very rare is called a boulder opal. This is easily distinguishable from the other two types of opal. Boulder opal is a thin strip of opal that is still backed by the host rock. The brown ironstone is a natural darkener for the thin clear strip of opal still attached to it. Boulder opal can also be mainly the polished ironstone that has cracks that are filled with veins of bright colored opal. The goal when selecting the highest grade boulder opal is to try to find a slice that has very few spots where the ironstone is seen coming through the thin layer when viewed face up. It is very accepted and usually common for the matrix, or ironstone to be seen in the gem. It is preferred to be less than 20% of the total surface to be considered a fine example.
The next thing is intensity and depth of color of the thin opal layer. Fine boulder opals can get quite costly with prices ranging from the more common white base opal and the rare black opal. These first three varieties of opal are all found in the ancient deserts of Australia. Opal does occur in Africa and the U.S., but more than 90% of the gems opal are mined in Australia. The fourth type of opal is actually not found in Australia.
Mexican Fire Opal is mined almost exclusively in the deserts of Mexico. Mexican Fire Opal is usually different from Australian Opal. Fire opal is a bright orange, almost tangerine, semi-transparent gem. Although Mexican Fire Opal is still a silicate and chemically identical to Australian opal, the differences are quite dramatic. Mexican fire opal has the impurity of microscopic hematite crystals that are infused in the crystal lattice promoting the orange color. The stone can either have no color play or some color play depending on the water content. Another big difference is typically fire opal is faceted like a typical gemstone, whereas opals are usually polished into a dome shape called a cabochon. When selecting a fire opal, the color can go from a light yellowy orange to a dark brown reddish orange. The preferred color is the true tangerine orange. The goal is to find the clearest gem possible. Fire opal is never 100% transparent. The milky feature is caused by the hematite and is part of the stone. A stone that is 80-90% transparent is very rare and highly collectible. The stones price out similarly to a fine white based opal.
HISTORY & FOLKLORE
Opal has a long and twisted history. Throughout the dark ages, it was a stone thought to possess magical powers. It was believed it could render its wearer invisible and could be used to cast spells on one’s enemies. It was highly regarded as the stone of kings. It was often used as an amulet around royal necks throughout history. Opal was highly valued until Sir Walter Scott wrote a book in 1829 called Anne of Geierstein. In the book, the maiden possesses a beautiful, magical opal that gives her great strength and beauty. In the novel, the opal starts losing its color as her beauty fades until at the end the stone loses all its fire and the maiden dies. The public believed in this tale and that opal got a reputation as a stone that was bad luck. It took 50 years for this stigma to fade and today anyone wearing a beautiful opal is considered pretty lucky! The best story of opal is it is said that after God finished creating all the other gemstones, he took his paint palette and scrapped it clean and threw all of the leftover colors into one magnificent gem.
Two side notes about other opals. The first is opal inlay. Inlayed opal is cut and fitted to an opening in a piece of jewelry, and then polished down to the surface of the metal. A typical white opal is usually used that is thin with a good fire. A black epoxy is used to secure the opal in place, but also has the additional benefit of creating a black-based look. The material used if fine grade material and in the most expensive inlay used. Another form of opal that was discovered in the mid-2000 is called Ethiopian Opal. The stone is proving to be unstable and although beautiful at first, it tends to lose its color over time.
WEAR AND CARING
Opal is a 5.5-6 on the Moh’s hardness scale making it a soft gemstone. Opal is to be protected and cared for. It should be worn with care and attention. Opals should not be exposed to direct hits as they can be chipped or broken. Opal is also porous and should be kept away from chemicals. Chroline and mild acids can etch into the gem. With proper care and tenderness, an opal will last a lifetime.
