"Radioactive Dating" isn't in the Yellow Pages

July 3, 2008 7:54 AM

Radioactive dating: Is it possible for a hobbyist to get something dated?

To make the story short, an old man died..and his kids just wanted to get rid of everything and sell the house and be done with it. On the curb with old shoes and broken tools was a magic basket of rocks! Everything in this basket is remarkable- so much so that I've become somewhat obsessed. I've had a ball reading about and identifying some of the samples, but there's a particular rock that's special. I don't know why, it's not pretty or sparkly or anything, just a flat, weathered stone that lives in my pocket now. I've decided that this rock is my own personal bit of deep time, my Lovecraftian nugget from the yawning chasm of antiquity. Is there any way to actually find out how old my pocket rock is?

posted by cometwendy to science & nature (7 comments total)

Call your local university's geology department. If they have the equipment, one of the grad students would probably be able to help you if you're nice.
posted by Green Eyed Monster at 8:03 AM on July 3, 2008

Talk to the geology department, but you probably won't need radiodating. They can generally figure these things out from other clues. But just to warn you...K-Ar testing is really expensive.
posted by Weighted Companion Cube at 8:19 AM on July 3, 2008

Hi, former geoarchaeologist here.
You can't carbon-date rocks. You can only carbon-date things that have organic material in them.
Even if you could date that rock (which you can with other techniques), I don't think it would tell you anything interesting. The rock material could be hundreds of thousands of years old, but the small piece of it that you have could have taken its pebble form at any point.

What would probably be more interesting to you is to take it into a geology department and see what kind of rock it is (no dating involved) and where it might have come from. They might be able to tell on sight, or they might have to flake a piece off with a hammer. Would you mind that?
posted by rmless at 8:56 AM on July 3, 2008

The word "carbon" doesn't appear in the post.

There are a dozen or more different elements that are used for geologic dating. Among the more common are K-Ar, Sr-Rb, and fission track analysis. All the methods require a lot of time by people who have a lot of student loan debt. The cost to you will be prohibitive.
posted by neuron at 9:32 AM on July 3, 2008

Before you make a habit of carrying that rock around all the time in
your pocket, you might check to see that it is not radioactive.
Likewise, don't keep your rock collection under your bed (same
advice for your old exotic lenses).

One day I came home after a semester at school, and found out
from my mom that the Department of Energy had confiscated by
"box of rocks" that I had been hauling around during my entire
childhood, because it was radioactive.
posted by the Real Dan at 12:09 PM on July 3, 2008

Maybe it could be dated isotopically, but it is unlikely to be done for free. Isotopic dates are expensive.

But without knowing anything about the rock, it's impossible to know whether it could be dated or not. If it is a sedimentary rock, it probably can't be dated. (If it is an organic rich shale, or has detrital zircons...maybe.) If it is metamorphic or igneous, it could be dated, depending on the mineral phases present.

So anyhow, I would give up on this idea, unless you are willing to invest time and money into pursuing a radiometric date. If you post some clear pictures I could maybe guess at whether it is dateable. But even then, nobody would do it for free-it takes expensive equipment and labor. Do you know anything about where the rock was found? Looking at published info about the area would probably be your best bet for learning something about it.
posted by HighTechUnderpants at 2:40 PM on July 4, 2008

Thanks everyone. I have finally managed to take a picture of the rock.
pocket rock
posted by cometwendy at 5:17 PM on July 4, 2008