Pure gold is not magnetic, a fact often used as a preliminary test for authenticity. Understanding the true magnetic classification of gold explains why a coin that reacts to a simple magnet is almost certainly a counterfeit. This scientific principle is the foundation of a quick, at-home method for separating genuine gold from fake.
The Magnetic Classification of Pure Gold
Pure, 24-karat gold is scientifically classified as a diamagnetic material, meaning it is not attracted to a magnet like iron is. This behavior is rooted in the gold atom’s electron configuration, where all electrons are paired within their orbitals. Since these electrons are paired, there is no net magnetic moment per atom, preventing the strong magnetic alignment seen in common magnetic metals.
When pure gold is exposed to an external magnetic field, it generates a very weak magnetic field that opposes the applied force. This results in a slight, almost imperceptible repulsion from the magnet. This subtle effect is far too weak to be noticed by a standard magnet and requires highly sensitive laboratory equipment to detect. Consequently, a pure gold coin appears completely non-magnetic when a simple magnet is brought near it.
Why Counterfeit Coins Are Magnetic
If a gold coin is attracted to a magnet, the reaction is due to the presence of other metals within the coin, not the gold itself. Counterfeit coins are often faked using base metals coated with a thin layer of gold plating. These core materials are selected because they are inexpensive and exhibit a strong magnetic attraction known as ferromagnetism.
The most common ferromagnetic metals used as filler or core material in counterfeit coins are iron, nickel, and cobalt. Even when gold is alloyed for durability, the percentage of magnetic metals is typically too low to cause a noticeable attraction. A strong pull from a magnet indicates that the coin contains a substantial amount of magnetic filler material, which completely overrides the subtle diamagnetic properties of the precious metal.
Practical Magnet Testing for Authenticity
The most straightforward way to test a gold coin at home is by using a powerful neodymium magnet, often called a “super magnet.” A genuine gold coin will show absolutely no attraction or stickiness when a strong magnet is held near it. If the coin noticeably sticks or is attracted to the magnet, it is a clear indication that it is a fake containing ferromagnetic alloys.
A more advanced application is the “slide test,” which utilizes gold’s diamagnetic nature. By holding the coin at a 45-degree angle and placing a neodymium magnet on its surface, a real gold coin will cause the magnet to slide down slowly. This delayed slide occurs because the moving magnet induces a subtle electrical field within the gold, which slows the magnet’s descent. If the coin were fake and non-magnetic, the magnet would simply fall off instantly.