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.
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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!
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