As a geologist and a skeptic, I’d like to debunk a popular myth: a diamond is not forever. This clever phrase was coined in 1948 as a marketing slogan for DeBeers, but I cry that it’s false advertising. Diamonds, formed at high-pressures deep within the Earth, are metastable in the low pressures at Earth’s surface. Over many million of years, the carbon atoms in the gemstones will rearrange, converting the diamonds into graphite. Pencil lead, essentially.

A real forever gemstone? Maybe zircon. There are zircons in places such as western Australia that are over four billion years old. Forever is a long time, though, and even zircons eventually degrade. Blue zircons can make really beautiful gemstones, though.

Okay, so maybe I am being too picky; perhaps I’m too much of a geochemical snob. On human timescales, diamonds appear to last forever. To prove a point, though, if I if ever became engaged, I want a peridot ring. Peridots are not forever gemstones. Actually, peridot is one of the most ephemeral gemstones. Peridot is olivine, which is the first mineral to weather in a rock containing this mineral. Olivine weathers quickly because the weak metallic bonds holding together isolated silicate tetrahedra are easily broken down by physical and chemical weathering.

But I like peridots much better than diamonds becaue they’re a beautiful green color, and they remind me of some of my favorite rocks, where peridots can be found. Sure, peridot is not as expensive as diamond, but I personally think that diamonds are overrated. Diamonds, with the possible exception of rare colored diamonds, are not worth what most people pay for them.

Diamonds are somewhat common, actually, and the market for the traditional off-the-shelf diamond engagement ring is artificially controlled. The economist might argue with me. Items are worth whatever people will pay for them. However, geologically, I just don’t see it. I highly recommend the book Diamond: A Journey into the Heart of an Obsession by Matthew Hart for anyone wanting to learn more about diamonds and the diamond industry. This book is an excellent quick read for anyone wanting some evidence that that diamonds are not really worth that much.

And I wonder: why all the hype about diamonds when there are so many other gemstones? Why should everyone have diamond engagement rings? Why can’t some people have zircons or sapphires or peridots, if they want to? Why is it “odd” (in the words of my grandmother) to have anything other than diamond?

Certainly, love and marriage are even more ephemeral than these gemstones, even highly-degradable olivine. These days, the typical marriage is lucky to last five years, so what does it matter which gemstone symbolizes your bond? Any gemstone is likely to last longer than your love. Peridot, one of the shortest-lasting gemstones (often degrading in hundreds to thousands of years), and diamond, one of the longest-lasting (degrading in millions of years), both will last much longer than the average or even the extraordinary marriage. Even if one is lucky and is married for sixty years or more, that peridot gem should still be going strong.

So, why diamonds? On human timescales they aren’t any longer-lasting than other gemstones, and they’re not particularly rare or valuable. I mean, how rare can they be when every young, engaged female has one around her finger?

Yet even my geologist friends, who appreciate the worth (or lack of worth) of diamonds, have diamond rings on their fingers or purchase diamond rings for their fiancees. I guess that so-called tradition might have something to do with it. A girl wants the diamond engagement ring, just as her mother and gradmother had. But are diamond engagement rings really traditional? Not everywhere, certainly. Diamond engagement rings are starting to catch on even in places such as Japan and China, where these rings certainly are not traditional. Why? Clever marketing, in my opinion.

Just a few days ago, a good friend of mine became engaged. Of course, she sent me digital photographs of the diamond engagement ring. I am quite happy for my friend. She’s marrying a great person, and she was so happy on the phone. I told her, quite honestly, that her ring is beautiful. I may not understand why a diamond ring is so important and necessary for an engagement, but I do understand why this ring is so important for my friend and why she is so proud to display it on her finger.

I wouldn’t begrudge her happiness nor the engagement ring she’s been dreaming of for years.
But for me, if I ever decide that it’s time to be married? Peridot. Or maybe zircon… or zoisite… or maybe alexandrite. No, peridot it is. Or maybe blue zircon… oh, I can’t make up my mind. Okay, peridot and blue zircon. But diamond? How conventional and boring!

An addendum:
I originally wrote this blog post back in December 2006. I met my fiance in June 2007, and we became engaged on Friday the 13th, March 2009. We didn’t realize that it was Friday the 13th until some friends pointed this out to us. Since the Friday the 13th superstition is ridiculous, we laughed it off. As a skeptic, I actually find it delightful that we became engaged on this “ominous” day. Almost two years later, we’re still engaged and plan to marry in October 2011. So far, no bad luck.

My peridot engagement ring is the top picture in this blog post. Yes, there are two tiny diamonds on either side of the peridot. My fiance, somewhat ironically, worked for De Beers at the time we became engaged, so he could not resist two teeny tiny diamonds. However, in a few months we will be resetting the ring (I’ll probably rid the ring of the diamonds) and designing a matching wedding band with more peridots. Because, at least for the fifty or sixty years we hope to be married, a peridot is forever.