What I've Learned

Diamonds used to be a girl's best friend. Perhaps they still are.

Though their friendship status may be uncertain, there are two things about diamonds that are sure: they are not formed from coal and they are not rare – certainly not rare enough to warrant the prices people pay for them.

I can take care of the coal myth in one short paragraph. Most diamonds that have been dated were formed before the Cambrian Period (about 542 million years ago). Coal is formed from plant debris and plants didn't appear on earth until around 475 million years ago. Diamonds, therefore, are millions of years older than coal. I rest my case.

So if diamonds are not formed from coal, where do they come from and what are they made of?

They come from deep in the earth – much deeper than coal – and are formed from naturally existing carbon. They get to the surface through volcanic action.

Not every volcano spews diamonds. In fact, the kind that do, deep-source volcanoes, are extremely rare; so rare that no one has actually seen one.

Here's what happens. Diamonds form in what are called diamond stability zones, about 90 miles down. These zones, where the temperature and pressure are just right for diamond formation, are not everywhere. They are thought to be primarily beneath the stable interiors of continental plates.

A deep-source volcanic eruption – again, these are very rare – shoots up, breaking off pieces of mantle as it goes and bringing them quickly to the surface. If these chunks of rock happen to be from a diamond stability zone, guess what? Diamonds end up on the surface. If the rocks containing diamonds erode over time, the gems can be found loose on the ground, but most often the gems have to be mined.

Mining diamonds is labor intensive. Many tons of earth have to be moved and processed for every carat of diamond that is found. Only about one diamond in a million is of gem quality. Most of the other 999,999 end up being sold for use in manufacturing.

If diamond stability zones are not everywhere and if deep-source volcanoes are extremely rare and if only one diamond in a million is of gem quality, the hard little sparkly things must be very rare.

So you are lead to believe, but it's not true. The supply far exceeds the demand. Any shortness in supply is artificially created by the diamond companies who hoard the stones and dole them out, selling them in small amounts to keep the prices high.

Are diamonds the hardest substance on earth? Yes and no.

Diamonds sit at the top of the Mohs scale of hardness. But hardness is defined as 'resistance to scratching'. Diamonds have the most stable atomic structure of all natural substances and are the most difficult to scratch. Nothing can scratch a diamond but another diamond.

That said, diamonds are also brittle. Take an expensive diamond and a penny and put both on an anvil. Smash each of them with a hammer and see which holds up the best. Okay, don't really do this, just take my word for it that the diamond will shatter and Abe Lincoln will only flatten slightly.

As I said at the beginning, diamonds used to be a girl's best friend. Here's what I suspect. Though our 16th president has a new-found reputation as an action hero – thanks to the movie, Abraham Lincoln, Vampire Hunter – if a girl is given a choice between the least coin in the rhelm and a diamond, she'll choose the one that's hard to scratch.