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Pyrite The Structure of Diamond Pyrite

Diamond is most commonly known as the gemstone traditionally presented on a ring in a marriage proposal. However, it's not just used during engagements and actually has a number of different uses! Diamond is the hardest known material, allowing it to be used in cutting and drilling tools (in the form of polycrystalline diamond, or PCD). It is also very good at transferring heat, having the highest known thermal conductivity, and so may become useful in electronics. It can be doped with boron impurities to provide electrical conductivity, potentially offering applications in sensors. And that's only just scratching the surface!

Diamond is made entirely out of carbon (y'know, the stuff your pencil lead contains) and is a giant covalent structure - made up of covalent bonds between the atoms. In a covalent bond, electrons are shared between the atoms, allowing them to attain a full outer shell (their happy place :P ).

Graphite, which pencil lead is made out of, is also a giant covalent structure containing only carbon. So, what's the difference? Why is one a shiny gemstone with all these crazy good properties, and the other a black substance. Well, it's to do with the way the atoms are arranged. In diamond, all the bonds between the atoms are strong, and there is a regular arrangement. In graphite, there is some regular structure, but it is in layers, which are only held together by weak interactions. Effectively, we are comparing a 3D structure to a 2D structure. Thus, there is a huge difference in the eventual properties of the two materials. Diamond's hardness and high thermal conductivity arise from the fact that all the bonds involved are strong and short.
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If anyone has any questions or comments about diamond, do fire away! I will probably update this soon with some more random facts about diamond. Thinking of doing how diamonds are made next, but we'll see!
Good start! I'll look forward to reading more :D

I guess I'll start by asking how easy it would be to snap a selfie stick made entirely out of diamond :P ?
(09-10-2018, 04:52 PM)Kyng Wrote: [ -> ]Good start! I'll look forward to reading more :D

I guess I'll start by asking how easy it would be to snap a selfie stick made entirely out of diamond :P ?

That would depend on the type of diamond used. Single-crystal diamond can actually be quite brittle, especially thin sheets of it. Polycrystalline diamond (PCD) is the diamond used in cutting and drilling tools. It it formed of a lot of different diamond crystals grown in together, and is much less susceptible to cracking. However, if the selfie stick isn't hollow (i.e. is made out of solid diamond), I'd expect it to be valiantly robust.

Am going to update this post later with some information on how diamonds are formed, in nature and in industry.
Nice :D

And roughly how much would that selfie stick be worth, based on the material it's made from? I guess it depends heavily on the type of diamond used :P .
I like this... but it's a bit beyond my understanding. Cool topic!
(09-30-2018, 11:02 AM)Kyng Wrote: [ -> ]Nice :D

And roughly how much would that selfie stick be worth, based on the material it's made from? I guess it depends heavily on the type of diamond used :P .

It would indeed - if you're making one out of synthetic diamond, it actually wouldn't cost all that much. Synthetic diamonds don't really have any intrinsic value - they're just carbon!! In fact, there's a lot of interest in the moment about being able to differentiate between synthetic and natural diamond, because De Beers have such a stranglehold on the natural diamond market.

Anyway, I said I would mention diamond formation quite a while ago, and I've finally decided to get around to it.

Diamonds are formed either in nature, or by intense industrial methods. The conditions required for these processes are very harsh, because under normal conditions graphite is the more stable form of carbon. For those interested, there is a line on a pressure vs temperature graph, above which diamond is the stable form of carbon - this is known as the Simon-Berman line. Note the intense temperatures and pressures that we are dealing with here!!
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These conditions can be achieved naturally inside the Earth's mantle, where diamonds are formed and then gradually rise towards the surface, where they are found. Synthetically, there is a technique known as high pressure, high temperature (HPHT) synthesis. This technique makes use of a press to achieve the high pressure required. The press is heated to above 1600 K, achieving a fairly high temperature. Graphite, or other carbon sources, are dissolved inside a liquid metal solvent (normally an alloy containing a high percentage of iron), which further aids the process. At the correct conditions, diamond can begin to precipitate out of the solvent and grow.

The other principle method of synthetic diamond formation is by chemical vapour deposition (CVD). In this process, a mixture of methane and hydrogen gas is passed into a chamber. Microwaves are fired at the gas molecules to create a plasma close to a substrate, which diamond seed crystals are already attached to. The radical atoms created in the plasma diffuse onto the diamond 'seeds' and grow, creating larger diamond crystals. This method still requires a high temperature, but only a low pressure, due to the formation of radicals.

These methods produce different signals in spectroscopy, depending on what defects/impurities have been incorporated into them. Natural diamonds may have metal atoms or clusters inside them, HPHT diamonds are normally yellow because nitrogen readily gets inside the press, whilst CVD diamonds often have a high hydrogen content, because of the presence of hydrogen inside the gas mixture. Synthetic diamonds have the advantage that impurities and other defects can be introduced for specific purposes, allowing the diamond to be 'tailored' for specific uses.
Unfortunately, your image isn't loading: I guess it's only accessible to students and people affiliated with the university :( . Is this what you meant to post?

Interesting post, though: I had no idea about diamonds being formed in the Earth's mantle and then rising :O . Are there any other gemstones that are formed in a similar manner, or is that not covered in any of your courses?
On the subject of diamonds, you might be interested to learn that a giant pink one recently sold for $44 million:

A crazy amount, perhaps, but it's undeniably beautiful!
And, another update - to inform you guys that the largest ever diamond found in North America has been unearthed. It's a 552-carat yellow diamond, and it was unearthed in Canada's Northwest Territories:

It's going to be cut and polished, but at this stage it's too early to estimate its value (which I'm guessing must be pretty high, in spite of the yellowness!)
Apparently, Louis Vuitton have purchased the world's second-largest rough diamond (a 1.758-carat monster):

The plan is to cut it up and turn it into fine jewellery. Probably for the best - since, while this diamond may be unusually large, it doesn't look like anything special in its rough state :P .