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  • [ ♪INTRO ]

  • When it comes to sparkly objects, the planet Earth has a lot to offer.

  • For examples of those, we usually think of mineralssolid structures made out of

  • repeating molecular patterns.

  • They've got a lot of cool properties, and if you put several minerals together, you

  • get a rock.

  • But there are also rocks that aren't made of minerals.

  • They're made of glassthat is, a solid that has a random, or amorphous, molecular

  • structure.

  • That doesn't mean they all look like a window pane or a phone screen.

  • Nature makes all sorts of glass, mostly out of a molecule called silica, or silicon dioxide.

  • But the variety of forms it can take might surprise you.

  • Here are five examples of natural silica glasses with some pretty rockin' origins.

  • Obsidian might be the most famous naturally-occuring glass.

  • Commonly referred to as volcanic glass, this dark, shiny rock is about 65 to 80% silica.

  • Most obsidian you'll see is black, which is actually due to the presence of microscopic

  • crystalline impurities that make the stone opaque.

  • But the presence of various impurities can produce different colors.

  • Iron oxide can give you reds and browns, microscopic crystals of a mineral group called feldspar

  • can create a rainbow of colors, and trapped gas bubbles can produce a golden sheen.

  • You might even see larger mineral crystals trapped inside, creating a snowflake pattern.

  • It takes really thick volcanic magma to make obsidian.

  • That's the stuff high in silica content.

  • Basically, the chemical bonds between silica molecules restrict movement, whereas if there

  • are metal ions present, they can break that structure and make the liquid rock flow faster.

  • So thicker magma equals more silica.

  • This silica-rich magma starts out with about 10% water content, but that water soon turns

  • to steam as the molten rock approaches the Earth's surface and it's no longer under

  • so much pressure.

  • That thickens up the magma even more, making it cool more quickly, and also stopping molecules

  • from arranging themselves into a crystalline structure.

  • So while obsidian can form above ground in a lava flow, most of it's made underneath

  • the surface, cooling and solidifying before it ever gets up here.

  • Opals may be the most colorful of gemstones, and the most well-known variety owes its rainbow

  • flecks to its amorphous structure.

  • Like many glasses, opals are made of silica, but these stones also contain water.

  • Yes, water can be a component of rocks.

  • They're made when water full of tiny silica particles, around 25 nanometers in diameter,

  • flows through and eventually gets stuck in cracks and pores in other types of rock.

  • Oftentimes, these silica particles grow like pearls, with shells of silica building up

  • layer upon layer.

  • This produces a wide range of sizes of silica spheres.

  • But if they're similar enough in size, as they continue to get deposited by flowing

  • water, they settle into a series of horizontal, parallel planes.

  • But after all that you still don't have an opallater, another collection of silica

  • particles has to settle into the voids between all the spheres.

  • It acts as a cement, and traps a lot of water along with it.

  • But that silica doesn't have a structured pattern to it, so our opal can't be considered

  • a mineral.

  • It's the spheres and the planes they lie in that give opals their optical properties.

  • In gemology, it's calledplay of color”.

  • Because of their different composition and structure, the silica spheres and the cement

  • around them bend light different amounts.

  • This creates what's called a diffraction grating, and splits white light into its constituent

  • colors.

  • But just like waves on the surface of a pond can interact with and interfere with one another,

  • so do the light waves inside the opal.

  • Some colors get amplified, and others canceled out.

  • Which colors we ultimately see depends on how big the spheres are.

  • If they're less than 138 nanometers in diameter, they only bend invisible ultraviolet light.

  • But once they hit that size, they produce violet.

  • And as they get bigger, the colors pass through blues and greens all the way to reds.

  • Red is actually pretty rare for opals, since it needs spheres over 241 nanometers in size.

  • But those large spheres also create all the other colors, which makes those opals the

  • most colorful, and the most highly valued.

  • If the spheres aren't uniform in sizeas little as 5% variationthey can't stack

  • into parallel planes.

  • Light still gets bent, but the overall diffraction effect gets canceled out within the stone,

  • so no pretty colors reach our eyes.

  • Most gem-quality opals are mined in Australia, but Australia is also home to the only known

  • specimens of opalized fossils, from crustaceans to dinosaurs to early mammals.

  • And opals have even been found in at least one meteorite!

  • But speaking of meteorites, when they're crashing into the Earth's surface can make

  • glass.

  • In the modern day, they're called tektites, from the Greek word for 'molten'.

  • However, the first written reference to themfrom over a thousand years agowas

  • Chinese for 'Inkstones of the Thundergods'.

  • Which obviously sounds way cooler.

  • Tektites come in sizes from tens of micrometers up to 10 centimeters long, and they're formed

  • when a meteor hits sandy or rocky ground and the energy from that impact heats up and melts

  • that ground around it.

  • Molten blobs are thrown up into the air, then cool into glass on their way back down.

  • For a lot of the 20th century, scientists thought they had extraterrestrial origins

  • that they were the glass version of meteorites.

  • One hypothesis in particular supposed that they had melted into glass on the Moon immediately

  • after an impact, been kicked off the surface with such force they escaped the Moon's

  • gravity, and fell down to Earth.

  • But if that were true, they'd be distributed a lot more uniformly on Earth's surface

  • than they really are.

  • Instead, they're found in a few regions called strewnfields.

  • **That's actually how types of tektites are named.

  • For example, Moldavite is named for the Moldau River in the Czech Republic, Australites come

  • from Australia, and Philippinites, well, you get the idea.

  • While there is quite a range, an average tektite is made up of around 70% silica, and has a

  • makeup somewhat similar to granite.

  • They come in shades of green to brown to black.

  • And they come in a variety of round-ish shapes, at least until erosion sets in.

  • Using our knowledge of radioactive decay, we can determine how old different tektites

  • are.

  • The oldest batch hails from Haiti and northeastern Mexico, dating back to the Cretaceous-Paleogene

  • transition — a geologic boundary coinciding with the extinction of the non-avian dinosaurs.

  • Which is also where you find the impact crater suspected to have been left by the meteorite

  • that did them in.

  • Meaning these tektites could be a 66 million-year-old relic of that very impact.

  • Another outdated hypothesis for tektite origins was lightning.

  • But there is a glass made by lightning strikes: Fulgurites.

  • They're what you get when lightning strikes wet sand.

  • Fulgurites are usually hollow tubes of fused silica, coated in sand.

  • And they're formed underground, sometimes running several meters in length.

  • That's because wet sand conducts electricity.

  • And a channel of lightning only needs to raise the temperature of the surrounding silica

  • sand to 1800 degrees Celsius to melt it.

  • That might sound like a lot, but a typical strike can raise temperatures on the order

  • of 1,000 degrees Celsius per second.

  • So two seconds is all you need.

  • Fulgurites are usually tan or black, but it depends on the material they're made from.

  • That includes impurities in the sand.

  • However, sometimes the lightning doesn't strike sand.

  • It hits a silica-based rock.

  • Which still creates a fulgurite, just a non-tube-shaped one.

  • If there's iron inside the rock's crystals, the lighting can actually add electrons to

  • convert it into pure metallic iron.

  • So throw in some shiny silvery color, too.

  • Based on exactly what the lightning hits, there are four classes of fulgurite.

  • Type one are 95 to 100% glass, basically entirely sand and made of thin glass walls.

  • Type two are made from clay and type four are from rock.

  • Both are up to 90% glass, but have thicker walls.

  • In these, the main component of the glass is an amorphous silica-based compound called

  • lechatelierite.

  • Type three fulgurites, at the other extreme end, are only up to 10% glass, and mainly

  • composed of a natural calcium carbonate-based cement called caliche.

  • Fulgurites form underground, but as the sand shifts, they can start to peek out.

  • And when they do, we can identify trapped gas bubbles from the time they formed, allowing

  • scientists to learn things like what kind of plants used to exist in the area long ago.

  • The first glass sponges appeared over 570 million years ago, and their descendants are

  • still alive today.

  • Yes, living glass.

  • Sort of.

  • Glass sponges belong to the taxonomic class Hexactinellida, and are unique among sponges.

  • They have syncytial tissues, which means their cells aren't specialized like ours are,

  • but rather merged together into one giant cell that can transport messages and materials

  • really quickly within the organism.

  • They're found world-wide, usually at depths between 200 and 3000 meters.

  • Most are slow-growing, taking over two centuries to grow a single meter.

  • The largest living ones, off the coast of Canada and Alaska, can reach the height of

  • an eight-story building!

  • As the name suggests, their tissues contain amorphous silica-based structures called spicules.

  • In some species, they fuse together to form a glass-based skeleton that persists after

  • the sponge dies.

  • And in one species, the Venus flower basket, this glass cage actually traps a mating pair

  • of crustaceans.

  • They enter when tiny, but eventually grow to be too large to fit through the gaps!

  • But it's not such a bad deal.

  • They clean the basket in exchange for food the sponges excrete as waste.

  • And one study of Venus flower basket spicules found that they transmit light similarly to

  • fiber optics butbecause they form at low temperatureshave added ions that

  • make them better at it than traditional commercial fiber optics.

  • And they also have internal structural braces that make them less brittle.

  • So it turns out that Nature is far more inventive with glass than you might think.

  • But so are we!

  • Without glass you wouldn't be watching this video.

  • Because humans took this simple concept of amorphous silica and crafted the vacuum tubes

  • that made computers run.

  • And later on used it to make circuit boards.

  • And monitors.

  • So let's hear it for glass in all its forms.