A Crazy Little Thing Called Zircon

In the midst of countless articles and e-mails about hateful tortillas, racist alma maters, banned students, the financial crisis, and the poor quality of food at Frank, I’d like to add a little color—the beautiful watermelon greens and reds of a mineral called zircon.

I’m a senior in the Pomona College Geology Department, and by a series of twists and turns I ended up wanting to know the age of a series of granitic dikes I collected in upstate New York. Don’t fear, Pomona, a dike is a planar intrusion of magma that cross-cuts host rock foliation, so try not to kill me for my slanderous vernacular. Back to the issue at hand, the reason for this desire is beyond the scope of this work, a frequently used phrase in scientific papers meaning I’m just too lazy to explain that part, so if you really care you can work through it yourself.

So here I am, I want the age of these rocks, but how can I find it out? Well, it turns out that there’s a pretty sweet radioactive system in these rocks, in which uranium turns into lead over the course of time, and if I measure that ratio carefully enough I can back-track to know when the system started decaying, which is the same time that the rocks cooled from red hot magma. Big problem, this system exists in this tiny mineral called zircon, a little devil of beauty that’s about a one in a million find in the zircon rich rocks of the world. I don’t use the phrase one in a million lightly; it literally has an occurrence of approximately one in a million.

Try not to get too upset for me, because I’ve already resolved this problem through the same separation method as many scientists before me, which I’m now going to explain:

I start with a sample of rock about the size of a basketball, if not bigger. I need to break this into slightly smaller pieces with a rock hammer, then throw these pieces into the jaw crusher, a terrifyingly loud machine that slams two textbook-sized metal plates together, pouring out pea-sized pieces of rock. From here we move on to the pulverizer, two rotating ceramic plates that eat these peas of rock and deliver to me a delicious beach sand of mineral grains. From here I head to the gold table, a giant green plastic machine that shakes violently with water running over its surface. As my sample slides down this table all the heavy stuff, zircon included, flies to the middle losing the lighter excess to the sides. It is the same design and concept as gold panning—coincidental name for a machine, eh? Where to next? To the horrible smelling and even more horribly carcinogenic methyl iodide heavy liquid solution… golly and how! I drop my sample through this yellow stuff and the low density material floats while my zircons and other dense mineral sink to the bottom. Next I use a giant magnet to pull off remaining zircon-free material leaving me with just what I want, for the most part. The time of separation is about six hours per sample not counting the intense cleaning that needs to be done to assure some false grain doesn’t slip into your pile. From the original basketball-sized rock, I’ll generally have less material than I can see in a small vial by this point.

Now the fun begins. I take these grains to Stanford University, home of one of two Sensitive High Resolution Ion Microprobe (SHRIMP) systems in the world. Grain by grain I mount these zircons on double sided sticky tape in small rows, then I cover them with a rock glue, embedding them in the bottom of a cylindrical clear plastic-looking disk. Polishing into the zircons is a must or the SHRIMP machine can’t read them, which is then followed by the long process of photographing the grains in reflected and luminescent light to see what parts of these small grains I plan to shoot with an ion beam to date them. The mounting takes three hours per disk plus overnight drying time.

Finally the process starts. I then head back to Stanford where for $2000 a day I shoot these tiny beasts until they tell me how old the rock is. By the way, in the spirit of time consumption it takes most of eight hours to work through each disk.

So, now are you ready for my opinions and the big reason why I’m writing this? Of course you are, that’s why you’re reading the opinions section. Besides the fact that I just got some great practice for a small piece of my thesis methods section, I just want Pomona students to take a second and appreciate the really important things in life… zircon separation and age dating.

Here at Pomona, we make huge deals out of everything we possibly can in an effort to add activist excitement to our lives. I ask, “why?” Why, when there are so many other fun and educational things on which our time could be better spent?

My advice is this Pomona students, do your best to enjoy your time here. While issues we constantly struggle with such as power dynamics, violent action, and racism are vitally important to deconstruct, please do your best not to get bogged down in them so much that you forget the real reason you’re here—to learn how to properly get blasted without it effecting your academics or your future adult life too much. The next time you’re feeling sad or angry with the Pomona College world, please just picture me staring down a microscope and looking for small elongate zirconium-rich treasures. You’ll feel better, I promise.

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