Monday, February 21, 2011

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: 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.

Figure 1. (Left) The Gibeon meteorite, from Namibia, weighs about 3,600 grams and is for sale at for $3,300.

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, such as

Before going further, here’s something you should know – these neodymium-based magnets are much more powerful than you’re used to. At, 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.

Here are some more links and some background information about neodymium magnets, found at

Rare Earth

“Neodymium magnets are a member of the Rare Earth magnet family and are the most powerful permanent magnets in the world. They are also referred to as NdFeB magnets, or NIB, because they are composed mainly of Neodymium (Nd), Iron (Fe) and Boron (B). They are a relatively new invention and have only recently become affordable for everyday use.

Grades of Neodymium

N35, N38, N42, N38SH...what does it all mean? Neodymium magnets are all graded by the material they are made of. As a very general rule, the higher the grade (the number following the 'N'), the stronger the magnet. The highest grade of neodymium magnet currently available is N52. Any letter following the grade refers to the temperature rating of the magnet. If there are no letters following the grade, then the magnet is standard temperature neodymium.


Neodymium magnets are a composition of mostly Neodymium, Iron and Boron. If left exposed to the elements, the iron in the magnet will rust. To protect the magnet from corrosion and to strengthen the brittle magnet material, it is usually preferable for the magnet to be coated. There are a variety of options for coatings, but nickel is the most common and usually preferred. Our nickel plated magnets are actually triple plated with layers of nickel, copper, and nickel again. This triple coating makes our magnets much more durable than the more common single nickel plated magnets. Some other options for coating are zinc, tin, copper, epoxy, silver and gold. Our gold plated magnets are actually quadruple plated with nickel, copper, nickel and a top coating of gold.


Rare Earth magnets have a high resistance to demagnetization, unlike most other types of magnets. They will not lose their magnetization around other magnets or if dropped. They will however, begin to lose strength if they are heated above their maximum operating temperature, which is 176°F (80°C) for standard N grades. They will completely lose their magnetization if heated above their Curie temperature, which is 590°F (310°C) for standard N grades. Some of our magnets are of high temperature material, which can withstand higher temperatures without losing strength.”

Neodymium Magnet Information

More background information about neodymium magnets:

Neodymium Glossary

More than you ever thought you could learn about magnetism and magnets. Here’s a full glossary with more details about magnets:

Picking a Metal Detector

Magnets are cheap and easy, but I’m planning to replace my old Minelab metal detector in the coming year. I’ve been haunting the websites of two manufacturers: White’s at and Fisher at

Getting back to the Meteorite Men, they had this to say on their website about their metal detector:

“If you've watched the award-winning series Meteorite Men on Science Channel, Discovery, Quest, or one of our other networks, then you've seen Geoff and Steve using the remarkable new Fisher F75. This extraordinary, top-of-the line detector is lightweight, perfectly balanced, extremely sensitive and the Meteorite Men's hand-held detector of choice. And it's a meteorite-finding machine.

The Meteorite Men used their F75s with great success at Canada's amazing Whitecourt Crater, at Gold Basin in Arizona, at the famous Odessa, Texas meteorite crater, on the search for the legendary Tucson Ring, and at many other secret locations. If you want to up the odds of finding your own space rock, then you need to be using the best equipment out there, and that's the F75.

The Meteorite Men are delighted to offer the very same unit that they've worked with throughout Season One and Season Two. Purchase directly from us and you will receive an exclusive color photo of Steve and Geoff, along with a genuine Sikhote-Alin iron meteorite (witnessed fall, Russia, 1947), so you'll know exactly what a meteorite sounds like when your detector goes over it.”

Cost is about $1,249. That’s a little steep for most of us to justify to our Chief Budget Officer, so they advertise a “starter” GoldBug for about $550.

The White’s GMT costs about $800. I logged onto their site and got this report:

“The White's GMT is a good choice for a low-end gold detector. By using the term ‘low-end’ I don't mean cheap quality, just low price. The GMT can be purchased for about $800.00 new and $500.00 used. It does have some problems with Arizona's heavily mineralized areas but can handle them decently with effort and practice. It can find gold as small as .02 gram with my experience and of course larger pieces. The fact that the GMT is a VLF or very low frequency detector means it can discriminate iron trash very well. In fact from my experience I'd say the discrimination is 99.9% accurate on trash. The digital scale normally shows gold at 25 or lower. What I am referring to is the digital ‘scale’ called ‘Probability of Iron’….

“The real upside to this unit is if you hunt old mine dumps or tailings piles. This is where the true dual purpose of this gold detector comes into play. While the more expensive pulse induction (PI) gold detectors will outshine the GMT or any VLF for the most part in the washes and hillsides, they won't be able to match the GMT's performance in mine dumps and tailings. Not only will the GMT find more gold in old mine tailings and mine dumps it will also tell you when a target is just an old nail or piece of iron junk accurately. It is also not affected by power lines like the more expensive PI units. It is also much lighter in weight than the more expensive PI units if that is a concern for you.

“So if you are looking for an entry level gold metal detecting gold prospecting machine that will do ok hunting washes and hillsides for gold and will absolutely shine in old mine dumps and tailings the GMT might just be the ticket.” (

Fisher F75 Special Edition

Alaska Mining and Diving Supply is a great spot for deals, background information, well-written stories, and more. As of this writing, they had a sale going on F75 units.

Fisher Gold Bug 2 - About $800

As stated above, this is a solid detector that works for meteorites, gold, and coins.

Coin hunting

I ran across a nice website recently devoted to coin hunting with a metal detector.

Figure 5. This 1875 Swiss half-franc silver coin popped up in southern Illinois recently. How it got there is a mystery… Check for more info about recent finds.

More Meteorite Links

Great information, and tons of links to keep you researching for days.

Good map and graph of known discoveries in the U.S.

A solid database of discoveries.

Delos Toole’s map of Arizona discoveries.

Claimed to be the oldest and best place to buy meteorites. Also has a key to determine if what you have is really a space rock:

University of New Mexico meteorite museum.

Recent meteor crater found with Google Earth.

Google Earth add-on showing 26,000 worldwide meteor impacts; in .kmz format.

Physicist Amelia Sparavigna of Politecnico di Torino in Italy found a 6-mile-wide crater in the Bayuda desert in Sudan using Google Maps, a free astronomical image-processing program she helped develop called AstroFracTool, and open source image-processing tool GIMP. The work appeared on ArXiv Aug. 3.


No matter what tool you’re using out there, practice and experience is a big key. Good luck!

Garret Romaine writes from Portland, Oregon.


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