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Let's go to ancient Egypt. This is the Egyptian pharaoh Tudin Common aka King Tut. And this was found inside his tomb. It's an ornate breastplate. And the piesta resistance is that gemstone in the middle. It depicts the god Raw as a beetle. But what kind of gem is it? And how did it form? For decades after the tomb's discovery in 1922, no geologist could find a solid answer. But now we have one. That gem formed because of a rock from space. Hi, I'm Sage and this is Crash Course Geology. They sparkle, they shine, and sometimes they're found in a literal treasure trove. I'm talking about gems. We value these stones for their distinctive qualities. They're hard to break, hard to find, and simply beautiful. And they
can be made of a bunch of different stuff. Most often they're composed of minerals, those inorganic materials that make up things like quartz, ruby, and garnet. Minerals have a specific crystallin structure. They're made of atoms that are arranged in an orderly repeating pattern. So that makes all minerals crystals. And when a crystal is valued specifically for its durability, rarity, and beauty, we call it a gem. No, Dwayne, you're not a gemstone. Yes, I still love you just the way you are. But gems can also be made of other stuff, including organic materials that come from living creatures, like a pearl from an oyster or petrified wood from a
tree. It all depends on what we deem valuable. Because of those qualities, people have been entranced by gems for a long, long time, coveting them, wearing them, attributing powers and curses to them, stealing them from palaces, graves, and renowned Parisian museums. Like people across the globe have treasured opals for centuries. Some indigenous Australians believe that they were left behind in the footprints of the creator who rode to Earth on a rainbow. So maybe it's no surprise we've always wondered where they came from in the first place or that Taylor Swift named a song after them. Technically, the song is Opelite and Opelite is man-made. Th this was a whole thing in the writer room. There was
Swifty on Swifty violence. We don't have time for it right now. We curious humans have been studying gems for thousands of years trying to figure out why and how they form. Like way back in the 70s CE, Roman philosopher Plenny the Elder was the gemstone expert. Some of his ideas were right, but he did say that you could only break a diamond by hammering it with a tool that had been soaked in goats blood. So, you know, grain of salt. But for a long time, that research was mostly guesswork. It took new technologies for us to find the answers we were searching for. Let's dig a little deeper. After the discovery of King Tut's tomb, it took another decade for someone to discover a similar gem in
nature. British surveyor Patrick Clayton found a bunch of yellow green stones in a part of the Sahara called the Great Sand Sea along the border of Egypt and Libya. He assumed it was a type of quartz. Later, the gem became known as Libyan desert glass. Geologists had a wide range of wild theories about the glass's origins, from lightning strikes to lunar volcanoes. As technology advanced, scientists have slowly teased out some clues. For one, researchers estimated that the Libyan desert glass was about 28 million years old. They uncovered evidence of its high pressure and high temperature beginnings. So high that some of the minerals within the glass, like the dark streaks of
Cristobolite, couldn't have possibly formed from ordinary happenings on Earth. They found chemical traces that suggest bits of iron from within the gem weren't from our planet. Essentially, the gem likely formed from meteorite slamming into desert sand, causing the sand to melt and recristallize along with those mysterious dark streaks. Put another way, the very same gem that was buried with an Egyptian king likely came from Earth tangoing with a space rock. But the mystery hasn't been completely solved. Some researchers think that the meteorite didn't actually hit Earth's surface, but rather broke apart in a lowaltitude explosion above it. Though there's still much to learn, it's safe
to say that we know a lot more about gems than we used to. Gemologists, scientists who study gems, use the MO hardness scale to measure a gem's hardness or resistance to scratching. They also study gems toughness or resistance to chipping or fracturing, and their stability or resistance to heat, chemicals, and light that can cause a gem's color to fade. Side note, you might have heard gems described as semi-precious or precious supposedly based on their rarity. But don't let those words fool you. There are so many exceptions to the rule, those labels are basically meaningless. Like, diamonds are considered precious gems, but depending on the type, they could be
worth less than supposedly semi-precious garnet. Aside from color, we've also ironed out some other qualities of gems, like brilliance, luster, transparency, and fire. Wow, Dwayne, you are dazzling. Did you get some work done? Modern geology has helped us learn a lot about where gems come from. They can form in many different ways, not just by meteoric explosion or your pet rock bedazzling itself. Some gems come from lightning like fulgrite, which forms when lightning strikes sand. And a lot of gemstones like emerald, aquamarine, and topaz form as molten rock cools super slowly underground. Other gems form similarly to how rock candy is made, just with minerals instead of
sugar. Hot water circulates through deep cracks in Earth's surface, dissolving minerals as it flows. When water eventually cools down, crystals like quartz and fluorite can begin to grow. Don't eat gems, though, even when they look delicious. And if crystals form in cavities underground, you've got yourself a geode, a hunk of rock lined with crystals on the inside. When layers of rock above it eventually wear away, that ball of crystals reaches the surface. Then you can crack that puppy open, see what sparkles inside. No, no, no. Don't worry. I wouldn't crack you open. Also, you're not a geode. There's nothing in there. However they form,
minerals all need the same basic things. The right temperature, pressure, time, space, and ingredients. Lots of those ingredients are pretty common chemical elements like silicon, carbon, and oxygen. But sometimes tiny traces of other elements get in there. Those impurities are often what determine a gemstone's color, which can sometimes change its name. Ruby and sapphire, two paragonss of gem high society, are actually just different colors of the same mineral, corandum. Other weird stuff can happen to baby gemstones, too, like the different colored bands in this watermelon termine formed when the environment around the growing crystals shifted. Or sometimes different fluids or gases get trapped in the crystal,
creating inclusions, like the needlethin hairs of the mineral routtile that form the star in this star ruby. Inclusions can also offer us information about where the gem formed geographically. For example, we can tell certain emeralds come from Colombia because of parasite inclusions in them. It's a type of mineral, not a flesh-eating bug. The more we humans learn about gems, the more fascinated we become. People today are just as into them as old King Tut, maybe even more. As of 2025, gemstones were a 36 billion industry, and the value of individual gems can really vary. Often gem sellers cut and polish them for sale, creating flat surfaces called facets that can enhance those
beautiful qualities like brilliance and fire. On the other hand, inclusions can make gems less valuable unless they're really cool looking like this rainbow lattice sunstone. But as early as the 1870s, scientists have tried to get around those long complex geological processes by making their own gems. Imitation gems known as simulants are made of materials that only look like certain gems. Think glass cut into the shape of a diamond or a hunk of granite covered in rhinestones. No, I said you looked great. But we've also harnessed science to grow gems that are so much like the real thing that they kind of are. These synthetic gems are grown in a lab by mimicking the conditions in which gems grow in the
wild. But the lab is way more efficient. In nature, rubies grow over millions of years. But in the lab, they can grow in as little as 3 hours. You also don't have to dig them out of the ground, which makes them a lot easier to come by. People still prize natural gems. The proof is in the price tag. But many are turning to synthetics as a more sustainable option. Processes that create synthetic gems don't use or degrade nearly as much land as natural mining does, though they do require a lot of energy. And gem mining can sometimes coincide with human rights abuses like forced labor and displacement of indigenous peoples.
These considerations are big and very complex. We've shared some resources below to dig deeper. As for how to tell if a gem was made inside the earth or in a lab, well, the average shopper probably can't. High-end gem dealers often send their wares to experts who use tools like microscopes, UV lamps, lasers, and X-rays to tell the difference. Whether we're coveting the sparkly jewelry worn by celebs at the Met Gala or perusing the crystal stand at the farmers market, we humans are mesmerized by gems. And that connects us to the people of the past who saw just as much beauty in them as we do today. As we move into the future of the gem trade, we'll have to ask ourselves even more questions about what we value and
why. Next time, we'll talk about one very special gem, diamonds. I uh see you then. Thanks for watching this episode of Crash Course Geology, which was filmed at our studio in Indianapolis, Indiana. Was made with the help of these rocking people. If you want to help keep Crash Course free for everyone forever, you can join our community on Patreon.
