Diamonds might be a girl’s best friend as Marilyn Monroe famously sung in the 1953 film “Gentlemen Prefer Blondes”, but that isn’t the only reason they are so highly prized. And just to get the other catchphrase out the way now, I’m sorry to announce that sadly diamonds aren’t forever as De Beers, the diamond-mining behemoth and England’s suavest spy, would have believe. Sorry, Bond.
Diamonds, at surface temperatures and pressures, actually decompose into graphite, the most stable allotrope of carbon on the Earth’s surface. Don’t worry if you’re buying a diamond ring though; the reaction is extremely slow, the transformation taking many hundreds of years.
So, chemically-speaking, why are diamonds valuable?
First off, although diamonds aren’t quite as rare as some would have you believe, they’re not exactly growing on trees. Yet. Diamond creation is actually one of the wonders of geology, the conditions for their production from carbon only existing at very specific temperatures and pressures deep within the Earth’s mantle. Typically at depths between 140 and 190km in the middle of continental plates where the conditions are just right. Microdiamonds can also be created at meteorite impact sites, but if you want the biggest haul then you’ll have to rock along to the nearest white dwarf star, whose cores are thought to be pure diamond.
Now, nobody’s mining at depths of 140km, so the only way the diamond ore gets out is via volcanic activity. Luckily diamonds have been forming for billions of years, so there’s been plenty of time for the magma to get to the surface. In fact due to the timespans, diamonds have been spread far and wide through processes such as glacial drift, alluvial deposition, and general erosion. You never know, there might be one in your backyard!
So that’s reason one: rarity–esp. the “purest” types.
The second chemically-based reason for diamond’s value is its unique properties. With a giant covalent structure that means every carbon atom in the lattice shares an electronic bond with four others, diamond is the hardest known bulk material in existence. As well as making diamond gems highly scratch-proof this also means diamond has important industrial uses in cutting devices.
And there’s more! Diamond also has the highest thermal conductivity of any bulk material–a property that hasn’t escaped the notice of the world’s computer manufacturers. Did you know that Apple now makes laptops with cooling systems based on diamond-like materials? All-in-all diamond is much more than just a shiny face or two . . .
And if you don’t want to root around in the mud looking for the next Star of Africa, there’s always synthetic diamonds. Days instead of millions of years. Autoclave versus Earth’s mantle. Doesn’t quite have the same ring to it, does it?