Rocks and minerals are known for being tough.

They’re the hard stuff that makes up the planet, and without them…well, we wouldn’t have much of a planet at all. Lots of the minerals on Earth started out life as liquids, either dissolved in water or heated above their melting point.

But occasionally, the minerals can form in such a way that preserves a few drops of fluid inside of them. This primeval liquid isn’t likely to replace your water bottle any time soon, but it is more than just a curiosity. It’s a window into the workings of the ancient Earth.

So let’s talk about the forbidden mineral water in these crystals, and why you should not drink it. [♪ INTRO] The majority of minerals on our planet crystallize from fluids beneath the Earth’s surface, and this crystallisation happens when the pressure, temperature, or saturation of the liquid reaches the Goldilocks point for mineral formation. And that perfect combo of temperature and pressure is different for each mineral. For instance, igneous minerals freeze out of molten lava when the temperature dips below their melting point.

Meanwhile, sedimentary minerals crystallize when the concentrations of their component molecules gets high enough. Crystals can begin to grow in a lattice within that fluid, building up a scaffold of atoms and bonds. But if there’s anything else floating around inside that fluid, it can interfere with the growing crystal, and cause imperfections in the 3D lattice.

That can make some parts of the crystal grow faster than others, which can sometimes result in a bubble of liquid missing the mineralization party. And as the mineral continues to grow, it seals the bubble inside. Most of this mineral growth happens deep beneath the Earth’s surface where temperatures are typically warmer, so when those minerals are brought to the surface, the rock cools down.

And when the warm liquid inside cools down, it contracts more than the surrounding crystal, creating a gas bubble that the liquid can slosh around in. Together, these liquid and gas bubbles trapped inside crystals are called fluid inclusions, and they can be found in a surprisingly wide range of minerals. You can find fluid inclusions in metamorphic rocks, in the form of carbon dioxide squeezed into a liquid by the high pressures at the bottom of the crust.

Lots of sedimentary minerals also preserve bubbles of groundwater and hydrothermal fluids inside them, too. Those bubbles can even contain crude oil. And it doesn’t stop at sedimentary rocks.

Water can get stuck inside igneous rocks as well. Gas bubbles are sometimes frozen inside amber. You can even find water and gas trapped inside glacier ice.

And yes, glacier ice is a rock, because it forms basically the exact same way as limestone does, by compressing lighter material down into one solid thing. In this case, snow becomes ice. In most cases, fluid inclusions inside crystals are very small, rarely measuring more than a tenth of a millimeter across.

But that doesn’t mean they can’t be useful to geologists. The presence of fluid inclusions in gemstones helps gemologists tell the difference between natural and synthetic stones, and can even help them determine where those stones formed. Mapping fluid inclusions in the field can also help in the search for mineral resources, since they can be a telltale sign of the hydrothermal systems that formed valuable ore deposits that we really want to find.

Plus, heating and cooling the inclusions can help to reveal their internal composition, without ever having to break the crystal. So these fluid inclusions can reveal all kinds of secrets about the ancient Earth. Because these bubbles trap air, researchers have been able to use them to sample the atmospheric gases during the Cretaceous, thanks to air bubbles stuck in amber.

They found that the concentration of oxygen was much higher during that period, and helped geologists chart its sudden drop from 35% to roughly 20%, around 65 million years ago. And hydrocarbon inclusions in old sedimentary rocks can give clues to the migration of petroleum through those reservoirs, which could help people find sources of crude oil. Despite their value to the world of science, the tiny size of these fluid inclusions means they rarely get the love they deserve.

But there is one kind of water-trapping mineral that has become fairly iconic: the enhydro agates. Agates are essentially colorful forms of the mineral chalcedony, which is a kind of fibrous microcrystalline quartz that forms from silica-saturated fluids. Agates can be many colors depending on the mineral impurities inside them, but the enhydro versions also contain water and gas on an impressive scale.

These mineral specimens are like fluid inclusions on steroids: they’re entire geodes that can contain enough ancient fluid that you can see it sloshing around, no magnification needed. Of course, you could break open the geode to let the liquid come flooding out, but then your water’s all gone and your enhydro agate becomes an ‘ex-hydro’ agate. Instead, if you polish your agate pebble juuuust right, to get close to the water pocket but not actually breach it, you can see the fluid moving around while keeping the pocket intact.

Now, the big bubbles in enhydro agates form in a very similar way to the microscopic kind. Agates typically form in spaces that were once bubbles in igneous rocks, crystallizing from fluids that percolate through those rocks. As the agate geodes grow from the walls of the rock bubble, some of those fluids get trapped inside.

Just like with normal fluid inclusions, geologists have tried to figure out the composition of enhydro agate liquid, in the hopes of learning more about their formation. For instance, in the state of Rio Grande do Sol in southern Brazil, enhydro agates are often found in Cretaceous age volcanic rocks. Since they had to have formed after the rock itself solidified, the agates are thought to be between 60 and 40 million years old.

Incredibly, when researchers drilled into some of these enhydro agates, they extracted what appeared to be bacterial cells. Not only that, but the cells seemed to be moving around erratically, suggesting that they were still alive! So had these agates preserved life, intact, from tens of millions of years ago?

Well, maybe. But also maybe not. Unlike the single crystals that trap fluid inclusions in an impenetrable mineral lattice, agate’s microcrystalline structure means its slightly porous.

That means that over time, fluids can move in and out of it. So the liquid that’s inside these enhydro agates may not be the same liquid that helped to form them in the first place. And when the researchers looked at the genes of the bacteria they got from their Brazilian enhydros, they found them to be closely related to the kinds of bacteria you get in tropical soils.

You know, the kind that you get on the surface… in Brazil. While the enhydro agates are porous to water, we’re still not totally sure if the gaps are big enough for bacteria to get in or out, so it’s hard to say whether the microbes inside are really really ancient, moderately ancient, or really not very ancient at all. Either way, the bacteria still offer a fascinating window into the agate’s long history.

And regardless of how old they are, they’re also why you should definitely not drink this particular type of mineral water. This month’s Rocks Box subscribers will receive their own enhydro agate from Indonesia, each of which is at least 5 million years old. And if you’ve been hoping to subscribe to our monthly Rocks Box deliveries but weren’t able to, you’re in luck!

We were able to open up some more subscriptions. How many are left when you’re seeing this? I genuinely don’t know, because we filmed this in December.

Head over to Complexly.store/rocks to see if there’s any left! You can also find lots of minerals a la mine cart, including our premium samples of some gorgeous fossil ammolite. Check all that out and more at Complexly.store/rocks.

Thanks for watching! [♪ OUTRO]