When you hear the word “Opal”, your mind probably jumps to the pearly white kind that’s commonly seen in US jewelry stores. But like many gemstones, Opal comes in different varieties, each with their own unique beauty! Today we’re going to take a closer look at Boulder Opal and find out what makes it so special! 

How are Opals formed? 

Before we jump directly into Boulder Opals, let’s talk about what Opals are and how they are formed. It’s important in understanding some of the key characteristics regarding their classification. 

Over millions of years, silica-rich water has seeped into the Earth’s crust to form Opals. If you’ve been following our blog, this may sound familiar, as most gems are made from a process of water meeting rock. But it’s the silicon’s shape that makes Opal special. Under a microscope silicon looks spherical, so the inside of an Opal looks like a cluster of little spheres. These spheres reflect light at all different angles, leaving gorgeous displays of color for the naked eye!

What is a Boulder Opal? 

Given the nature of its formation, Opal is very porous and contains quite a bit of water. Unfortunately, this makes Opal vulnerable to wear and tear. However, Boulder Opal is naturally attached to ironstone and is therefore more durable. The ironstone doesn’t just aid in durability; it also acts as a backdrop to the Opal, making the colors really stand out. So when you look at a Boulder Opal, the “front” will be a stunning display of colors, and the “back” will look like a regular rock. Sometimes you will even see remnants of the ironstone displayed on the front of your jewelry. 

Boulder Opals vs Doublets

Since Opal is so fragile, many jewelers will glue cuts of Opal to other materials such as obsidian, ironstone, or even industrial glass. When Opal is artificially adhered to another material like this, it’s known as a doublet. Doublets are still good quality and do contain real Opal, but it’s important to note that the adhesion is not natural. So if you consider yourself a gemstone purist, you’ll want to shop for Boulder Opals, which have the natural backdrop of ironstone. These natural Opals can still be treated by a jeweler to be more durable. So don’t shy away from these unique beauties!

Where in the world is Boulder Opal? 

Opals are found all over the world, from the Western United States to Brazil to East Africa. But the leading producer of Opals is Australia, and Australia is the only place to mine Boulder Opals. 

Since they can’t be found anywhere else, Boulder Opals are quite rare and expensive, although not as much as Black Opals. Boulder Opals are better quality than doublets, but they are usually less expensive than Black Opals. Black Opals also have a dark “backdrop stone”, usually influenced by carbon and iron oxide. To the naked eye, Black Opal and Boulder Opal can look very similar. So if you love Black Opal, but aren’t ready to invest your life savings, consider Boulder Opal instead. 

The Beautiful Colors of Boulder Opal 

Although Black and Boulder Opal look similar, Boulder Opal doesn’t have the same richly contrasted color. Boulder Opals tend to display a lot of medium-hue blues, reminiscent of Turquoise or Caribbean waters. But you may see a range of different blues. Due to the spherical structure of Opals, you’ll also usually see more than one color at play, and you may catch any color of the rainbow. Typically, Opals with the richest colors and with the most colors present are the most valuable.

A large teardrop shaped opal with blue and green hues is set in an 18k yellow gold bezel with chain detail and four granulated prongs. The pendant hangs from a delicate chain.

This Boulder Opal necklace is one of our favorites, because it displays an array of colors within one striking gemstone. 

Why is Boulder Opal so expensive? 

Boulder Opals may be strikingly beautiful, but that’s not the only reason they’re expensive! They’re also the second most rare Opal in the world, and they’re not so easy to mine. Mostly found in Queensland, these gems aren’t available to mine anywhere outside of Australia.

Boulder Opal mining is a grueling process that requires a lot of machinery and attention to detail. The mines are enormous, and the Opals usually appear as little cracks on the surface. After excavating, miners have to mechanically saw open the removed boulders to reveal the hidden Opals. They might spend all day excavating with no significant Opals to show for it. So the next time you admire your Boulder Opal, thank a miner! 

How to Care for Boulder Opal 

Since Boulder Opals have a layer of ironstone, they are not as fragile as solid Opal. However, they are still a porous gem and should be kept dry, even if they’ve been treated. They are also only a 5.5-6.5 on the Mohs hardness scale, which means they are susceptible to scratching. So keep them separate from other gems and remember to remove them before any damaging activities. For more jewelry care tips, make sure you check out our Jewelry Care blog here.

Which Boulder Opal is for You? 

Boulder Opal jewelry can range anywhere from dainty to bold! Here are a few of our favorite Amáli pieces and who we’d recommend them for. 

A model wears a small rectangular opal ring set in an 18k yellow gold chain wrapped bezel with four granulated prongs.

The modest size of this Boulder Opal ring makes it perfect for someone who appreciates the finer things in life, but prefers them to not be flashy. Sparkly, but not over the top, this ring is an ideal everyday piece. Just don’t forget to wear with caution! 

A rectangular opal with blue, purple and green hues is set in an 18k yellow gold bezel wrapped in chain with four beaded prongs on a thin ring band.

This larger ring, on the other hand, is a bold statement piece with phenomenal patterns! It’s hard to believe this stone is natural, because the colors look painted on. We recommend this ring for someone who wears vibrant outfits and dances to their own tune. 

A model wears a small Boulder opal earring set in an 18k yellow gold chain wrapped bezel with four beaded prongs. The stone hangs on a French hook closure.

There’s something fantasy-like about these Boulder Opal earrings. Although they’re modest in size, it’s hard not to be entranced by the color combination, especially against the 18k gold bezel. If you spend your time reading and daydreaming, these earrings may just be your perfect match! 

Hopefully you’ve gained an understanding of Boulder Opals, and maybe you’re even ready to seek one out yourself! Remember to shop with reputable jewelers so you don’t end up with a synthetic or lookalike. At Amáli the stone comes first, so we are happy to answer any questions about our gemstones!