Opals may just be one of my favorite stones on the planet. They feature such a riot of color, the best ones invoking the most coveted abstract paintings. It's true that no two stones are identical, but with opals you can actually see this in action. Each one has its own unique appeal, and it really is personal preference when it comes to purchasing one. They're supposed to bring good fortune to wearers, and the Ancient Greeks thought they imparted to their owners a gift of prophecy.
Unlike most gemstones, opals are a product of Earth’s yearly changes. Life-giving seasonal rains soaked into dry, silica-rich, semi-desert land and carried that silica deep down into the rock. As the year turned and the rains gave way to the dry season, that water would slowly evaporate, leaving behind these tiny (and do I mean tiny) silica spheres within the cracks in the bedrock. Now, do this for a few million years, and the resultant product is an opal vein. These veins of opal can be absurdly thin. Like, the kind of thin where they disappear if you look at them sideways. This is why you'll often see opals with protective layers (as in doublets and triplets) or even with the much sturdier rock matrix the opal is attached to (Boulder opal).
So cool, right, but how in the world do itsy bitsy silica spheres turn into the riots of color patterns opals can produce? Turns out size really does matter. Spheres sized 0.1 microns bend light violet, 0.2 microns bend red, and the rest of the rainbow falls in between. For reference, a human hair is ~75 microns, while red blood cells ~5 microns. Yeah, I did say those spheres were small. Massive personality though.
While there are beautiful opals found around the world (Mexico, Ethiopia, Europe, etc.), the most well-known certainly hail from Down Under. Australia is the best-known source for black opals. The play of color shows up best against the dark body color. Opals have been mined commercially there since around the 1890’s. Some of the mines have amusing names, too. Coober Pedy is said to mean ‘white man in a hole’ in one of the local Aboriginal languages. The best black opals are said to come from Lightning Ridge, Australia, an apt name. The Bedouins thought opals contained lightning, my personal favorite opal mythos.
Regarding care, opals should be treated gently. Due to its porous nature, avoid getting any lotions or soaps or sprays on them. Additionally, don't expose opals to high heat, light, or dry conditions. Remember, up to 20% of opal structure is water, so you don’t want to trigger any undue evaporation. Most opals are cured to prevent the cracking that can occur if they dry out, but to be on the safe side avoid storing opals in dry areas. You can always put a small cup of water in a safe or box to help keep avoid a drop-in humidity. This works well for pearls, too!