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A Gem of a Compliment

Posted by | February 24, 2010

A scientific friend I work with paid me a compliment last summer that still rings in my little head. She said the garnet earrings I had on that day looked good. It was true (I modestly admit), but that’s not what impressed me. She next asked if I had found the garnets myself.

Now that’s the way to make geologists really appreciate you as a human being. Give ‘em credit for a good find!

Garnets are my favorite gems. I guess that’s because it’s not really that tough to bring back good garnets at the end of the day in many localities across the U.S. There are many spots in the country you can take children garnet hunting with guaranteed success, something that obviously cannot be said of diamond quests.

And once kids get hooked (or you do), there are lots of ways to move up the ladder of difficulty – because there are no less than six basic types of the gems and because some beautiful garnets are exceedingly rare.  Even some of the common garnet types have spectacular features – something that can put some zing into the hunt.

In the rough, most undeformed garnets have 12 sides. (The crossword puzzle term for that form is “dodecahedral.”) A photographer friend I work with just gave me a nice dodecahedral garnet he found. The example I’ve got on my desk is dark purple, but garnets vary from purple or red to essentially any color of the rainbow. (When they are attacked by rain and the elements, they turn a bit brown on the outside, but the 12-sided shape remains quite clear.)

Near my home in the Northwest, we have the sole locality in North America for what’s known as star garnets, and they are the state gem of Idaho. They are dark purple, and you might not pay much attention to them stepping over them in the field, thinking them to be much like other garnets.

But if you polish a star garnet into a dome shape (called a “cabochon,” another term that can turn up in crosswords), you’ll see a star of light as you turn the gem around in your hand. The fetching effect comes from a different mineral, one that grows in a needle shape, that’s inside the garnet. The fortunate flaw, if you will, creates a special effect with light that improves the dark garnet immensely. While no star-garnet is as valued as a good diamond, they are seriously sought after and occasionally sell for tidy sums.

But garnets are much more than pretty baubles to geologists. When we’re lucky, they tell us information about the time and pressure history of a rock. Their chemical composition can function like a thermometer, one that gets “stuck” at the high temperature so we can still read it even when we’re holding the cool rock in our hands. All of that is really useful to geologists, because we are basically historians – we want to know the history of the planet, including the temperature history of metamorphic mountain-building episodes, meteorite impacts, and more.

It might surprise you to learn that chemists can make garnets in the lab these days – just as they can make rubies and sapphires. Personally, I think the gems that we humans make are “real” gems. Plus, they are generally a lot purer than Mother Nature’s, quite magnificent to behold. So before you fork over any significant amount of money for the Earth’s garnets – or any natural gemstone – you might care to spend some days meditating on the deep philosophical differences between value and cost.

With all the money you save by not buying natural gems, you’ll have plenty to finance good camping trips next summer to look for mica, garnets and other common minerals – just for the sheer joy of the hunt.

And in the meanwhile, if you live in the parts of the country that have been hit hard by this tough winter, you’ll have some great summer day-dreaming to see you through the last of our dark evenings.