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martyb [soylentnews.org] writes:

The BBC is running a story World's largest blue star sapphire 'found in Sri Lanka' [bbc.co.uk]. This single stone has been certified as weighing 1404.49 carats (about 280g; nearly 10 ounces) with an estimated value of approximately $100m. By comparison, Sri Lanka's entire gem industry "is worth at least £70m ($103m) annually." The previous record holder weighed 1395 carats.

What I found even more interesting was the story behind it; also from the BBC: How the world's biggest sapphire grew so large [bbc.com].

First off, what is a sapphire? According to the article:

"Sapphires are so hard because they are formed from corundum, an aluminium oxide. "Corundum is the hard gritty stuff used as an abrasive in emery paper," says [University of Cambridge mineral scientist Simon] Redfern [cam.ac.uk].

"If you add just a trace of iron and titanium to the mixture of aluminum and oxygen from which the corundum is growing, it forms as sapphire. So sapphire is 'dirty' corundum - corundum with a trace of iron and titanium."

So now we know the ingredients to a blue sapphire, what is the recipe?

Making sapphires is a lengthy process. This particular sapphire would have formed within the rocks of Sri Lanka's highlands.

[...] The rocks are mostly granites, which form when molten magma cools and solidifies. But they have been subjected to intense heat and pressure.

"The granites have been dated as almost two billion years old, and were subsequently squeezed and re-worked in a massive metamorphic mountain-building episode that happened more than 500 million years ago," says Redfern. "Temperatures and pressures deep within the roots of these mountains would have reached more than 900C and over 9000 atmospheres pressure."

And now, you know!

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