We’re so accustomed to seeing rocks everywhere we look that we often assume they’re all pretty much the same. After all, what could be so interesting about a little stone lying on the ground, right? Yet, if we take a closer look, we can sometimes find they’re more special than they initially let on.

Take opals, for instance. They might not look like much at first glance, what with their unsightly, craggy exterior, but it’s their incredibly beautiful interior that makes them so desirable. Once you learn what makes them so special, you’ll wish you had your own…

This might seem like an ordinary rock you would find in any park or back yard, but when you take a closer peek, its true nature begins to emerge. It’s no ordinary stone—it’s an opal! Though they’re nothing special on the outside, their interior reveals wonders…

1. Opals are basically an optical illusion: When gazing at the beautiful interior of a refined opal, what you’re looking at is essentially a naturally formed optical illusion. The reason is that light is actually unable to pass through the stone at all…

Instead, the light gets refracted by perfectly aligned tiny spheres of silica inside the gem. In turn, these spheres trick the human eye into seeing a bright spectrum of colors that change with every possible angle.

2. Opals are made from rain: While it’s never been officially concluded one way or the other, many experts have long believed that opals form after rain seeps into the tiny pores of the rock! But that’s not all…

This theory surmises that, after all the water that has made its way into the core of the rock finally evaporates, it leaves behind a kind of silica gel. And once that silica is completely dry, it hardens and transforms into an actual opal!

3. Opals come in a wide variety of different colors: Opals can reflect every single color of the rainbow, which lends to their popularity as jewelry. White opals are the most commonly found, while black ones are the rarest.

4. The majority of opals exist in Australia: Experts suggest that roughly 95 percent of the world’s opals are found here. They’re usually mined in the town of Coober Pedy in South Australia. It makes sense that the opal is the country’s national gemstone.

5. Ancient Romans saw opals as a sign of hope and good fortune: In 75 C.E. one unnamed Roman scholar admitted to being mesmerized by the gem’s colorful, kaleidoscopic effects. Also, he had some pretty loving words about the gem…

Some opals carry such a play within them that they equal the deepest and richest colors of painters. Others… simulate the flaming fire of burning sulfur and even the bright blaze of burning oil,” the scholar wrote.

6. Australian Aborigines recognized the importance of opals: It has been long written that the Aussie Aborigines believed the opal to be a sign of the “creator’s” touch. They also believed opals were created at the end of a rainbow to allow harmony on Earth.

7. Opals exist on other planets: That’s right—opal is one of only two gemstones that have ever been found away from the Earth! With looks so out of this world, it only makes sense that opals have been discovered in space. But where?

In 2008, NASA officially announced that it had detected opal deposits on the Red Planet. Many people believe this discovery is further evidence that the planet once sustained life, which makes sense since opals require water for their formation.

8. Opals appear throughout Greek mythology: Not only were the ancient Greeks convinced that the opal had innate prophetic powers, but they also believed they were formed from Zeus’s tears of joy after he defeated the Titans.

9. Opal is the birthstone of October babies: If you’re looking for a great gift to buy a friend born in October, look no further! Not only does the opal symbolize hope and purity in metaphysics, but it’s also commonly regarded as a protective stone, which makes sense when you think about how its rough exterior protects its beautiful inside.

10. You have to have a keen eye to be an opal miner: Opal miners need to be able to recognize the stone’s characteristic streaks of color, which indicate the presence of the precious gem concealed within. That’s no simple task in a dark mine!

11. Some people think opals are bad luck: Not everyone believes that opals represent positivity and hope. In the 1800s, some marketers in the gemstone world began claiming the stones were actually bad luck. Nevertheless, the notion never really caught on.

12. Opals were important to a prominent figure in British royal history: Queen Victoria admitted her favorite gemstone was the opal. And that’s saying a lot for a woman who had the most expensive diamonds, rubies, and sapphires at her disposal!

Now, the next time you see that pile of rocks on the ground, you’ll realize you should probably take a closer look. Who knows? One of them might actually be a precious stone!