Carry Magnet Go Hunting for Gold?
A man called our offices recently and asked, “A magnet isn’t going to tell me anything about gold, right? I mean, only ferrous metals are attracted to magnets, so what’s a magnet going to tell me anyhow?”
We never like to criticize our callers, but it seems this gentleman was suffering from a few mistaken ideas about magnetism. First of all, he was not 100% correct when he said that “only ferrous metals are attracted to magnets,” because nickel and cobalt are slightly magnetic too.
Second, our caller was not correct when he said that a magnet wouldn’t tell him anything he needed to know along when he went hunting for gold. In fact, a magnet really can provide some valuable information in situations like these…
A compass needle isn’t nearly as strong as many of the permanent magnets used today. But the physical process that magnetizes compass needles and chunks of neodymium alloy is essentially the same. It relies on microscopic regions known as magnetic domains, which are part of the physical structure of ferromagnetic materials, like iron, cobalt and nickel. Each domain is essentially a tiny, self-contained magnet with a north and south pole. In an unmagnetized ferromagnetic material, each domain’s north pole points in a random direction. Magnetic domains that are oriented in opposite directions cancel one another out, so the material does not produce a net magnetic field.
You find an old gold coin and get excited by your discovery…however you then discover that it is attracted to your magnet. The attraction is a sure sign that the coin you are examining is not made of pure gold; it is made of gold (or some metal that looks like gold) that has been plated over an iron core. So there – your magnet has told you something important. Good thing you brought it along.
You find a beautiful old gold chain that your magnet picks up…but then you notice that only the clasps on the end of the chain are attracted to the magnet. That tells you that those end pieces are made of gold-plated iron pieces. But don’t jump to conclusions then and decide that the gold chain that is not attracted to your magnet must be made of karat gold. It might be made of gold that has been thinly plated onto some other nonferrous metal, probably silver.
Magnets and the Process of Elimination
Those are only a few of the processes you can go through when you pack a big strong magnet and go hunting for gold, or for silver, platinum and other precious metals. Actually, you are not using a magnet to find precious metals, you are going to use it eliminate items that are not.
In magnets, on the other hand, most or all the magnetic domains point in the same direction. Rather than canceling one another out, the microscopic magnetic fields combine to create one large magnetic field. The more domains point in the same direction, the stronger the overall field. Each domain’s magnetic field extends from its north pole into the south pole of the domain ahead of it.