Description
Blue opal is a variety of the gemstone opal that comes in shades of blue and blue-green. Note that the term “blue opal” sometimes refers to a mostly opaque, teal-colored variety of common opal found in Peru.
Peruvian blue opal is such a staple of the country, they made it their national stone. Peru and its neighboring country Brazil are also known for the increasingly rare Paraiba opal, a bluish-green variety resembling the color of sea glass. Beyond South America, where does blue opal come from? Slovakia and Indonesia produce blue opal, while the United States has opal mines in Nevada, Idaho, and Oregon. Oregon’s Owyhee opals were a recent find, displaying soothing light or dark shades of pastel blues. Blue opal gemstones are not a mineral, like other gemstones, but an amorphous mineraloid. Meaning, the chemical composition is composed of microcrystalline silica spheres that layer to refract the blue light spectrum! Blue opals come in both common and precious varieties. Precious opals show play-of-color, while common opals don’t. Peru produces both types, with some specimens containing small zones of color play.
Blue is pretty rare in nature, which begs the question: Is blue opal natural? Yes, the earth creates opals in stunning blue hues. Like any opal, blue opals consist of microscopic, hydrated silica spheres. The size and proximity of the spheres determines which opal color we see because of how light bounces through the crevices between the spheres. Blue opal color comes about when the spheres are smaller (whereas larger spheres produce red or orange opal.) Sometimes, mineral inclusions contribute to natural blue opal color. With Peruvian opal, for instance, secondary copper inclusions lead to the blue-green coloring.
Is blue opal rare? While this calming hue is a fairly common opal color, quite a few of blue opal’s traits set it apart from other gemstones. The stone belongs to its own “Opal” species, rather than the “Beryl” or “Quartz” family, for instance. Common blue opal emits a type of iridescence called “adularescence.” Adularescence refers to a glow that appears to be inside the stone, instead of on its surface. The only other gems to possess this trait are moonstone and sometimes rose quartz. In terms of durability, this gemstone ranks at a 5-6.5 on the Mohs scale of mineral hardness, similar to turquoise or hematite.
