What is Fool's Gold? - YouTube

This video has been sponsored by Nord VPN. Right  now they're offering 75% off 3 year plans, as  

well as one month free, which you can get by going  to nordvpn.com/nilered. As a kid I can sometimes  

remember looking through dirt, and finding little  bits that looked almost like gold. And almost  

every time, I would get really excited thinking  that I was rich or something, only to be quickly  

shut down, and told that it was worthless fool's  gold. At the time I kind of just accepted that  

answer, and I threw away what I had found, without  really questioning much. What I didn't know though  

was that despite it being way less valuable than  gold, it was still a really interesting compound.  

The mineral name for fool's gold is pyrite or iron  pyrite, and its chemical name is iron disulfide.  

It's chemical formula is pretty simple just FeS2,  but what makes it really cool, is the different  

ways that it can crystallize. The appearance that  it ultimately takes on, will depend heavily on the  

environment that it was formed in. Some important  factors that affected, are things like purity,  

time, pressure and temperature. For example  pirate from a certain region in Spain, tends  

to form these oddly perfect looking cubes, which  honestly still kind of look fake to me. Their size  

and distribution can also vary quite a bit, and  some crystals can get really big like this one.  

The base unit cell that builds the pyrite  crystal is cubic, and under these circumstances,  

the macroscopic crystal that formed, was cubic as  well. However, impurities and the other conditions  

that I mentioned earlier, can alter how these  units build on each other, and it can affect the  

final appearance. So depending on where you are in  the world and what the geological conditions are  

in that place, it can look quite different. For  this video, I'm gonna be focusing on pyrite, but  

I did want to mention that it is possible, for the  iron disulfide to have a non cubic unit cell. It  

can instead be something called orthorhombic, and  when this happens, it forms a different mineral  

called marcasite. This one's a lot more brittle  though, less stable, and has a different color. In  

any case, now that we know a bit about what fool's  gold is in general, I want to dive a bit more into  

its physical and chemical properties. So to start  off just in appearance and feel, I think it's  

really similar to metal, and color wise, it can be  close to that of gold, and it's also often found  

in the same area as gold, so it's not surprising  that they can sometimes get mixed up. The biggest  

difference though, is that gold is never found  as these sharp and highly ordered structures,  

and it's usually just found as an amorphous chunk  like this. And another major difference is that  

gold is really soft and malleable, whereas pyrite  is really hard and brittle. So if it's hit with  

something like a hammer, the pirate would shatter  into pieces, whereas the gold, would just get  

flattened. Also in terms of its density it's only  around 5 grams per cubic centimeter, whereas gold  

is about 19.3. With small quantities it might be  hard to tell, but once you get a decent amount of  

the pyrite, the weight difference is pretty  obvious. So when a big chunk is found it's  

relatively easy to tell a difference, and it's  only really an issue when you have lots of small  

bits. For example here, in a clip that I found on  YouTube, it really does look like gold. However  

this was only because the really shiny pyrite  was reflecting a lot of the light from the sun,  

and making it hard to tell its color. Once he  moved to the shade though the brassy yellow color  

of the pyrite became quite evident, but the color  of the gold stayed the same. His other simple test  

was based on the fact like I mentioned before,  that the density of pyrite is way less than that  

of gold. Just by gently swishing around the  water, the heavier gold is able to stay put,  

but the lighter pyrite is moved around. From its  overall metallic and shiny look, a lot of people  

would think that it's conductive and, well they're  right it kind of is. It's not nearly as conductive  

as a proper metal though, and it's classified  as a semiconductor. In general, semiconductor  

materials are used pretty extensively in the  electronics industry, and it has been suggested,  

that pyrite might have some use there as well.  Currently I think the major use of it related to  

things that are electronic, is in non-rechargeable  energizer lithium batteries. In this battery,  

one of the electrodes is the lithium itself and  the other one, is made by coating iron disulfide  

on a thin layer of aluminum. Okay so now for the  fun part, where I get to play around with it,  

and learn more about its chemical properties. It  would have been insane to sacrifice my really nice  

cube so instead, I bought a bunch of ugly ones  from eBay. I really don't remember exactly how  

much it cost, but it was quite cheap, and probably  only around $20 for the whole bag of them. For  

the first test, I just put a small amount of  concentrated hydrochloric acid, on one of the  

pieces. I let it sit there for a few minutes,  but it didn't look like much was happening.  

There should have been a reaction going on, but I  just think it's really slow. The iron disulfide is  

FeS2, but I thought that it might react faster  if I converted it to just FES. This can be done  

pretty easily by just heating the pyrite to its  decomposition temperature, which starts at around  

540°C. To do this, I just carefully shot it with  a blowtorch until it looked like the surface was  

turning black. Some pieces of pyrite also started  cracking off, but I'll talk about that in a bit.

When it cooled down, I added the HCL  again and the effect was very subtle,  

but it was there. Like last time, I left  it for a few minutes and when I removed it,  

almost all of the blackness had disappeared.  The HCL had also taken on a yellow color,  

which you can see on the paper towel. So the major  thing that happened here was a reaction between  

the black FeS that I made, and the hydrochloric  acid. This lead to the formation of Fe(ii)Cl,  

as well as hydrogen sulfide gas. The amount that  was reacting here was so little though that it  

wasn't really possible to see any gas coming off.  However I wanted the effect to be much clearer so  

I decided to try heating the pyrite more, and to  convert as much as I could to the FES. Initially  

it looked decent and the whole surface was turning  black but then suddenly, pieces of it started to  

shoot off. I'm not 100% sure what caused this, but  I think it is a direct result of the decomposition  

of the FeS. In order for it to break down to FES,  it needs to kick off a sulfur. It's fine if this  

happens on the surface of it because the sulfur  just boils off, and then burns in the air to make  

SO2. However if this happens in the cube, there's  no place for the sulfur gas to go. So I imagine  

that it starts building up pressure, and it  eventually gets to a breaking point. To a certain  

extent there's also probably some water mixed into  the mineral, which also can cause it to explode. I  

continued heating the large piece that remained  and initially some pieces did come off of it,  

but eventually it stopped. I'm not exactly sure  why it stopped breaking apart, but I'm assuming  

that it was somehow able to release some of the  gas pressure. I kept heating it until most of  

it had become red-hot, and then I let it cool  down. As it cooled, the surface of it slowly  

got oxidized by oxygen in the air to make what I  assumed was red Fe(iii)2O3. When it eventually got  

to room temperature, I thought that it was pretty  interesting, because it didn't look like the  

fool's gold at all anymore. There was absolutely  no goldish yellow color left, and it was all just  

black and red. Like I just said, I think the  red stuff was Fe(iii)2O3, but I'm not sure  

if the black stuff was FES, or Fe(ii)O. I tried  testing it again, by just adding some hydrochloric  

acid to the surface of it, and it kind of just  soaked it up. If you recall from before though,  

when I tried this with the intact pyrite, the acid  just sat there. So apparently as it decomposed,  

it got a lot more porous. I broke it apart  with a hammer, and what I thought was cool,  

was that it was possible to see all the different  layers. On the outside was the fully reacted and  

oxidized stuff, but then right underneath it was  a layer of black FeS. Then just below that was  

the still fully intact FeS2. I really thought that  the heat penetrated much deeper, but apparently it  

didn't. Onto this I tried adding the hydrochloric  acid again, and it worked a bit better. It was  

possible to see a small amount of bubbling, but  it still wasn't as good as I would have liked it  

to be. To get it to react vigorously, I would need  to convert a lot more to the FES. And to do this,  

I first had to crush it up. This really isn't  very hard to do though, because the pyrite is  

actually quite brittle. So I just added some of  it to a mortar, and started bashing it. This was  

what I had after a few minutes, and I probably  could have crushed it a bit more, but I figured  

this was good enough. This was all added to a test  tube, and I did my best to flush it with nitrogen.

Then just like all the other times I blasted it  with a blowtorch. The reason I used the nitrogen,  

was that I hoped without any oxygen present, the  sulfur would be able to come off, and knock it  

immediately converted to SO2. After only heating  it a bit, it all started turning black, and I  

could see that there was a gas being released  from the powder. Because of the background it  

was hard to see, but there was also a white  vapor that had filled the tube. At the time,  

it didn't occur for me to test it, but it was  almost definitely sulfur maybe along with a  

bit of water vapor. What I think is cool, is that  industrially, pyrite is used in a very similar way  

to this, to generate elemental sulfur. Depending  on the purpose, the sulfur can be kept as is,  

or can also be converted to SO2 for  the paper industry, or even to SO3,  

to make sulfuric acid. When I felt like most of  it had converted to FES, I stopped heating it,  

and I let it cool. I probably should have  refilled the tube with nitrogen though,  

because as it cooled, the surface was oxidized  and it turned red. I figured this was fine because  

most of it was still black, but then I mix things,  and saw there was still a whole bunch of pyrite.  

I apparently had the same issue as before, where  it only really converted the stuff on the outside,  

and the stuff in the center, was more or less  intact. This time though, I thought I still  

made more than enough, so I continued on with  the testing. When it got to room temperature,  

I dumped it all onto a dish, and it honestly  kind of looked the same. Nonetheless I took a  

small sample of it, and I placed it onto another  dish, and tried adding hydrochloric acid again.

This time the reaction was way more vigorous,  and a gas was definitely being produced. H2S  

is extremely potent, and even in small quantities  it smells like rotten eggs. So a very simple test  

for it, is technically just to try and smell  it. This was all done in my fume hood though,  

which apparently worked quite well, because I  didn't smell anything. The only real way for me to  

smell it would be to bend over and to get really  close to it. The problem with this though, is that  

H2S is also super toxic around the same level  as cyanide gas, so I wasn't too excited about  

trying to take a breath of it. The much smarter  thing is to instead use test strips. These are  

made pretty easily by soaking paper in a solution  of lead acetate, and then letting it dry. Now if  

I was in fact making H2S, then the lead acetate  on these strips, should be able to react with it,  

to make black PbS. And when I did this, that was  exactly what happened. I was making the H2S here  

mostly as a demo, but in general it is a useful  chemical. In the lab, it's usually produced the  

same way, where a strong acid is reacted with FeS.  However the FeS is rarely made from pyrite, and  

it's usually either purchased, or made directly,  by reacting iron and sulfur powder. It leads to an  

extremely exothermic reaction, and this is a clip  from one of the first videos that I ever posted  

to this channel. The videos that I made back then  were totally different, but if you're interested  

in checking it out, there's a link in the  description. In any case I think that's about it,  

pyrite might not be as nearly as valuable as  actual gold, but I think it has enough of its  

own unique properties and uses, that it more than  makes up for this. And honestly, I think the cheap  

price is actually a good thing, because it means  that most people can buy it relatively easily.  

For example, I think the large cube sample that  I have, is one of the coolest things that I own,  

but it only cost me something around $100. In  Canadian dollars, that's about two grams of gold,  

which is not only not very much, but also nothing  really impressive to look at. In any case,  

this was the first video that I did on a mineral  and I had a lot of fun doing it. I definitely plan  

to do this again with another mineral, so in the  comments, let me know what you'd like to see. I  

ended up getting really behind schedule editing  this video, so I'm probably gonna be posting it  

from the airport, on my way to Japan for vacation.  To do this though, I'll have to connect to the  

public airport Wi-Fi, which isn't really secure,  and kind of makes me nervous. However luckily,  

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they're offering a great deal, that gives you  75% off their three-year plan, as well as one  

extra free month. You can get this by going to  nordvpn.com/nilered, or by clicking the link in  

the description. As a side note, some of you might  be wondering why I'm posting the video on the way  

to Japan, and not when I get there. My answer to  this is kind of simple, where A I don't really  

want to be working on videos once I get there,  and B I just think it could be fun. I'm gonna be  

having a 14 hour plane ride between Minnesota  and Tokyo, and I just thought that it could  

be interesting, to buy Wi-Fi and to answer your  comments from the air. As usual a big thanks goes  

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