Back in the 1840s, the California hills were crawling with miners seeking
their fortune in the gold rush. Prospectors would rush in to stake their
claim on glittering mineral deposits, but all too often, they found pyrite instead, hence the more common name of fool’s gold. But fool’s gold might not
be as foolish, or worthless, as those prospectors first thought. We can actually use it to get our hands on some really useful stuff, like sulfur and copper. And thanks to some recent discoveries, it may even help us mine real gold, after all. [♪ INTRO] The name pyrite comes from the
Greek word ‘pyr’, meaning ‘fire’, because it makes sparks when
it’s struck against metal. And it’s a really simple mineral. It only has two ingredients, iron and sulfur. Inside, those elements can be
arranged in a few different isometric crystal structures, from
cubes to octahedrons or dodecahedrons. So pyrite crystals can look like half of
the shapes in a set of table top dice. It’s also thought that these shapes
could have been the inspiration for the Platonic solids that ancient
Greek philosophers, including Plato, believed were the basic elements of the universe. Those early philosophers would have
certainly had plenty of opportunity to study pyrite crystals, since it’s a pretty
common mineral in all kinds of rocks. You can find it in mineral
veins, coal seams, stalactites, and around the edges of magma intrusions. It can even be produced biologically
by certain kinds of bacteria, and it’s not uncommon to find
entire fossils made of pyrite, which are stunningly cool to look at. So, with so much of it around, it’s no wonder that people have tried so hard
to find uses for the stuff. In the early 1500s, pyrite put the fire in
some of the earliest firearms in Europe. These wheel-lock guns would
rub a serrated steel wheel against a piece of pyrite to make the
sparks, which ignited the gunpowder. It’s the same idea as modern
lighters that use a spark wheel, or those strikers you may have used to
light your Bunsen burner in chem class. Just with pyrite instead of the
flint that’s more common today. But pyrite’s most important application is its use in the exploration and exploitation of ores. An ore is defined as any natural rock
or mineral from which a valuable metal or other material can be extracted. And despite what video games may suggest, there’s not just one ore for each material. Pyrite is a great example of an ore
for something we use all the time. Weirdly enough, it’s not iron, even
though pyrite is chock full of the stuff. It’s much easier to extract iron from
oxide minerals like hematite and magnetite, so processing pyrite for iron is
basically more trouble than it’s worth. But pyrite is a much better ore for
its other main component, sulfur. Pyrite is the most abundant
sulfide mineral in the world. And sulfur compounds have a ton
of industrial and commercial uses. For instance, sulfur dioxide is used as a
food preservative and a bleaching agent. And sulfuric acid is the most widely
used industrial chemical of any kind. It’s used to make fertilizers, car
batteries, explosives, and much more. Now, to release that sulfur, you start
by roasting your pyrite at around 600 degrees Celsius, which
causes the sulfur to burn with oxygen in the air to make sulfur dioxide. Then you just add water, and
you’ve got sulfuric acid. And historically, pyrite was a critical
source of the sulfur for all of this. But these days, we collect most of the
industrial sulfur we need as a byproduct of the petroleum industry, so pyrite is not
the king of that particular smelly hill. We do still use pyrite in the
ore processing industry though, thanks to one of its crystal sisters. One of the most important ores for
copper is a mineral called chalcopyrite, which often forms alongside
pyrite in the same deposits. The problem is that chalcopyrite is
also mixed up with other minerals that are totally worthless, at least
if your goal is to smelt some copper. A common technique used to separate
chalcopyrite from the other minerals is to grind everything up really
small and add it all into water tanks. Metal-bearing particles are slightly hydrophobic, so they will attach to air
bubbles and float to the surface, making what’s kind of a copper-rich foam, while other minerals are
carried away in the water. Sounds great, but there’s a
trick to getting it just right. When the particles are ground too fine,
it’s harder for them to get into the foam because they’re too small
and miss the air bubbles, meaning that as much as 15% of the copper
in the chalcopyrite gets washed away. And this is where pyrite comes in! Researchers have found that specially
treated ground-up pyrite particles can act like a pool floaty for
the super-fine chalcopyrite. The fine particles will stick to the pyrite crumbs and get transported up into the
foam, saving them from getting lost. The scientists think this new process
could allow them to recover almost all of the copper in a chalcopyrite deposit. All thanks to a little pyrite shuttle! Which brings us to the
coolest use for pyrite of all. So-called fool’s gold might actually
be the key to finding real gold. The two often form together,
especially in mineral veins, so pyrite can help traditional
prospectors zero in on gold deposits. Plus, pyrite tends to oxidize
when exposed to the air, creating a distinctive rust-colored
deposit called a gossan. This gossan tells miners where those pyrite
and potentially gold-rich mineral veins reach the surface, and where they should drill. But it gets even better than that. In some cases, pyrite itself can contain
small but significant amounts of gold. These can be tiny inclusions
within the pyrite crystal that have become trapped as the
two minerals have grown together. And sometimes iron atoms can even
get replaced by atoms of gold in the crystal structure to make a kind
of alloy within the pyrite mineral. Now, while it is technically possible to
extract this gold from inside the pyrite, you’d have to do some pretty major processing, which takes a lot of energy and money. So you’d have to really want that gold. But scientists have recently discovered
a third way that gold and pyrite can be neighbors, which could make
it way easier to separate them. Using a high-resolution atom probe, researchers built a 3D map of the elements
inside pyrite’s crystal structure. And they saw that gold atoms can
concentrate wherever there are imperfections in the crystal lattice, which happens when
pyrite is deformed at high temperatures. That causes atomic bonds to slip and
become misaligned, which lets the gold in. The researchers think that those
gold clusters could be a target for a more environmentally friendly
extraction method called bio-leaching, and you’re not gonna believe the twist here. Bio-leaching out the gold would
rely on rock-munching bacteria that can break down the crystal around
the already-weakened dislocations. And once it’s broken down, you can just pop out the gold that’s left
behind and run off to the jeweler. So what was once thought to be just a junk mineral during the Gold Rush may turn out
to be as cool as the real thing. Speaking of a gold rush, if you want
your own beautiful piece of pyrite, you should hurry to SciShow.Rocks to sign up for our SciShow Rocks Box subscription. Every month, we send our subscribers a
high-quality, ethically sourced mineral that has its own fascinating science
story, which we tell with these videos. But the subscriptions do fill up fast, so check it out soon if you’re
interested, and thanks for watching! [♪ OUTRO]
