Eli5: Why are lab-grown gemstones still relatively small?

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I think the largest disclosed un-certified gem right now is a 155 carat diamond. Which, sure, it’s a big gem. But if it was possible to make unreasonably large gems, we’d be seeing one-piece emerald kitchen counter slabs on the market right now and people with enough means would be making gemstone windows.

So, why is the largest synthetic gemstone still ‘only’ palm-sized? Is it a matter of scaling the size of equipment? The cost of materials? Some inherent fragility in the gems once they reach a certain size?

In: 16

The largest synthetic gemstones are actually **HUGE**.

We can grow some single(!) crystals such as quartz and sapphires that are way beyond anything natural, in the hundreds of kilograms, and that at an extreme purity. Or with a precisely controlled impurity to give them a certain color: pure sapphire is transparent like glass, add 1% chromium to make it a red ruby (yes, ruby is just a variant of sapphire), or add 0.01% iron to make it blue, and many other colors.

Alexandrite and emerald can also be grown quite well, but it is a bit more complex and thus more expensive. And unlike sapphire, they have a less wide use in industrial and consumer applications, adding further to the cost and lack of interest to optimize their size. Meanwhile, large so-called boules of sapphire are used for very sturdy “glass” (not really a glass), and ruby is used for lasers.

Diamonds however are quite finicky, they need quite extreme conditions to grow. Even more if one wants them to be extremely pure so that they are perfectly transparent. It is also not clear what a very large diamond is ultimately useful for beyond what the much cheaper sapphire can do; the little bit of extra hardness doesn’t do that much. There are however some applications as thermal conductors, as diamonds are the best one known.

Define “Gem”

Lab grown sapphire blocks can be as big as a brick and commonly used for viewport protectors as it does not scratch easily

Lab grown ruby rods are used in lasers and can be as thick as my wrist.

Lab grown diamonds have their uses too, but those applications are usually small, so lab grown diamonds are also usually small.

The answer to any, “We have the technology, why doesn’t it exist?” question is almost always, “Because no one actually wants it.” (Or more accurately, “No one wants to pay for it.”)

Like, you assume that *surely* some eccentric billionaire out there would pay any sticker price for a comically huge lab-grown gem, but like, *would they, really*? It does have to compete with all the other stupid crap they could buy instead, like a yacht, or investing it somewhere it will grow and make them even more money.

Also, this isn’t Minecraft. You can’t just build a countertop or a window pane out of diamonds and expect it to perform those functions well. Whether a gemstone has the correct strength properties to maintain being machined into that shape and stay there, hold up against forces like people leaning against or sitting on it (for the countertop), hold up against wind and rain battering against it, whether it meets energy emission standards (for the window), or even just a question of if the gem can be mounted in those places due to its own weight… there’s a lot of open questions, and all the while trying to justify them you have the nagging question over your head of, “And why exactly did I not just go for the material that already exists, is significantly cheaper, is more widely available, and works better in every way?”

Diamonds require very particular conditions, but we can already grow other gems far beyond the size of a palm.

https://res.cloudinary.com/engineering-com/image/upload/sapphire_boule_01_f0hlst.jpg

That picture is from 2015 and the two cyllinders to either side of the guy are lab grown 300kg (1.5 million carat) sapphires.

Full Article:

https://www.engineering.com/story/new-technique-grows-worlds-largest-sapphire-crystal