Precious metals are metallic elements, including gold, silver, and the six Platinum Group Metals (PGMs), distinguished by their rarity and high economic value. These metals possess unique physical and chemical properties, one of which is their behavior when exposed to a magnetic field. The magnetic response of any material falls into three main categories: ferromagnetism, paramagnetism, or diamagnetism. Ferromagnetic materials, like iron or nickel, exhibit a strong attraction to magnets. Paramagnetism and diamagnetism describe much weaker interactions that categorize the majority of precious metals, and this classification is ultimately determined by the configuration of their electrons.
Gold and Silver: The Diamagnetic Majority
Gold (Au) and Silver (Ag) are the two most widely recognized precious metals, and both fall into the category of diamagnetic materials. Diamagnetism is a property where a substance is weakly repelled by an externally applied magnetic field. This repulsive force is exceedingly subtle and often imperceptible without highly sensitive laboratory equipment. For this reason, pure gold and silver items appear entirely non-magnetic in a casual test using a common magnet.
The underlying cause of this behavior is the electron structure of the metal’s atoms. In both gold and silver, all the electrons are completely paired, meaning they spin in opposite directions, effectively canceling out any inherent magnetic moment. When an external magnetic field is introduced, it induces a temporary, opposing magnetic moment in the electrons. This induced field always opposes the external field, resulting in the slight repulsive force that defines diamagnetism. This weak, negative magnetic susceptibility is a defining physical characteristic of pure gold and silver.
Platinum and Palladium: The Paramagnetic Exception
Platinum (Pt) and Palladium (Pd), which are part of the Platinum Group Metals, display a different and less common magnetic property known as paramagnetism. Paramagnetic materials are weakly attracted to a magnetic field, an effect that is significantly stronger than the repulsion seen in diamagnetic metals. However, this attraction is still far too weak to be felt by hand or to make the metal stick to a standard refrigerator magnet. This weak attraction immediately distinguishes them from common ferromagnetic metals.
Paramagnetism arises because the atoms of these metals contain unpaired electrons. Unlike the paired electrons in gold or silver, these unpaired electrons possess a net magnetic moment. In the absence of an external field, these atomic moments are randomly oriented, resulting in no overall magnetism for the bulk material. When a magnet is brought near, the external field causes a slight alignment of these individual atomic moments, momentarily magnetizing the metal and causing the weak attraction. Palladium has the highest magnetic susceptibility among the PGMs, and other PGMs like Rhodium (Rh) and Iridium (Ir) are also paramagnetic.
Practical Application: Using Magnetism to Detect Fakes
The distinct magnetic properties of pure precious metals provide a simple, non-destructive method for screening potential fakes. The principle of the test relies on the fact that an authentic item will either be weakly repelled (diamagnetic) or weakly attracted (paramagnetic). If a piece of bullion or jewelry strongly sticks to a magnet, it is definitively not pure precious metal.
Counterfeiters often use common, inexpensive metals like iron, nickel, or steel as a core because they are strongly ferromagnetic and readily available. If a magnet immediately grabs the item, it contains a significant amount of a ferromagnetic material, making it an obvious fake. A more sophisticated counterfeit might use tungsten, which is paramagnetic like platinum, but the overwhelming majority of fakes rely on the strong attraction of a ferromagnetic core.
Using a powerful neodymium magnet allows for a more effective test. This strong magnet might demonstrate the subtle diamagnetic repulsion or the weak paramagnetic drag, particularly when the item is placed on a tilted surface.