Meteorites, Magnets, and Metal Detecting

I’ve probably been watching too much “Meteorite Men” on the Science Channel. I’m starting to see little rusty rocks everywhere I go, and since I visit a lot of gravel bars in the course of rockhounding and gold prospecting, I’m getting nervous that I’ve passed over a valuable piece of space debris. If you haven’t caught meteorite fever yet, try this website: http://meteoritemen.com and check out the stories there. You can even purchase a space rock of your own, such as the Gibeon fragment from Namibia worth about $3,300, shown in Figure 1.

Meteorites, Magnets, and Metal Detecting

Meteorites, Magnets, and Metal Detecting

In one of the latest episodes, the two meteorite hunters traveled to the Atacama Desert in Chile to visit a known “strewn field” where they had found fragments in the past. Many times, they use metal detectors for their work, including one time when they rigged up a giant ten-foot array detector that they towed behind them in a Kansas wheat field. They found a huge space rock about six feet beneath the soil thanks to that contraption.

This time, they rigged up a drag board fitted with dozens of powerful rare-earth magnets, and hooked it to their pickup truck. They repeatedly raked the red desert floor and managed to attract dozens of little pieces of iron, worth between $5 and $10 per gram. They also devised another big array detector and found a larger piece, worth almost $20,000.

We all know there are about 31 grams in a troy ounce, and with gold at about $1300 per ounce, that works out to around $40 per gram. Some of the very rare pallasite meteors are worth about the same amount.

Obviously, a metal detector that can search for gold and iron would be a nice purchase. More on that in a minute. My low-tech solution was to purchase a used golf putter at the local Goodwill store, and pick up a fancy round magnet at one of the many online sources.

Before going further, here’s something you should know – these neodymium-based magnets are much more powerful than you’re used to. At www.UnitedNuclear.com, they provide this warning:

“Neodymium magnets are very powerful, much more powerful than magnets most people are familiar with and need to be handled with proper care. The magnetic fields from these magnets can affect each other from more than 12 inches away. Please note that these magnets are fragile. Even though they are coated with a tough protective nickel plating, do not allow them to snap together with their full force or they may chip, break, and possibly send small pieces of metal flying on impact. Our magnets can easily bruise fingers and the larger ones can break finger bones and even crush hands as they attempt to connect together.”

I can attest to that, but the way. I had two rectangular neodymium magnets about two inches long, an inch wide, and a half-inch thick. They looked like fat dominoes. Or, one still does. When I was dinking around with them, they flew together with a loud “clap” and one of them busted into halves, with additional fragments flying around. One went whizzing past my ear like an angry hornet, and another carved a deep scratch in my finger, drawing blood. On that same Atacama desert episode of “Meteorite Men,” prospector Steve Arnold got his fingers pinched between two magnets and he, too, donated blood.

MY NEW MAGNET
So, here’s what I put together, as shown in the figures below:

Figure 2. (Left) Giant neodymium-based ring magnet. You can see it’s been dragged through the dust already, and has picked up some magnetite, black sand, or iron.

Figure 3. (Right) Used golf putter with various magnets attached to the head of the club, and the big ringed magnet sitting on top. Total cost was about $40.

Figure 4. Trash, black sands, and hot rocks picked up around the campfire. Nickel is for scale – magnets don’t pick up most coins.

Famed comedian W.C. Fields once observed there were two ways to travel: first-class, and with children. I sometimes feel the same way about camping. Kids are great fun, and opening up a world of science and discovery is a treat. But the way they run around without any shoes, risking a rusty nail and subsequent tetanus shot, is enough to drive me crazy. I’ve decided I can justify dragging my putter magnet around the campfire a few times because I’m sure to clean up a lot of rusty nails and other trash. I’m a one-man camp cleaner. You can see one of my hauls in Figure 4. In the more popular US Forest Service campgrounds, I’ve run a quick pass over the gravels where I park, and I’ve picked up quite a few nails from perilously close to my tires.

Do permanent magnets have a half-life or otherwise “decay” over time?

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