Diamagnetism of Gold
Also: diamagnet, magnetic susceptibility (negative)
Diamagnetism describes the weak repulsion of a material by an external magnetic field; gold is diamagnetic and is therefore not attracted by magnets.
Gold belongs to the group of diamagnetic materials: when placed in an external magnetic field, it is minimally repelled rather than attracted. This effect is so weak that it remains invisible in everyday life — yet it is of great importance for the authenticity testing of gold coins and bars.
Physical background
Diamagnetism arises from the induction of small circular currents in the electron shells of an atom when an external magnetic field is applied. According to Lenz's law, these induced currents generate a magnetic field that opposes the external field — the material is repelled. Because all of gold's electron shells are fully occupied and there are no unpaired electrons, it lacks the permanent magnetic moment required for paramagnetism or ferromagnetism. The result is a negative magnetic susceptibility of χ ≈ −3.4 × 10⁻⁵ (SI, dimensionless).
Diamagnetism is temperature-independent and very weak — in contrast to paramagnetism, which follows Curie's law, or ferromagnetism (e.g. iron, nickel, cobalt), which produces strong attraction.
Importance for authenticity testing
The magnet test is a quick, first-line, non-destructive testing method:
- A powerful neodymium magnet does not attract genuine gold.
- Strong attraction points to ferromagnetic contamination or core fillings (a classic method for detecting tungsten counterfeits).
- Caution: Non-magnetic metals such as brass, tungsten or lead also pass the magnet test — so it does not rule out counterfeits entirely.
For a robust assessment, the magnet test should always be combined with density measurement using Archimedes' principle or an X-ray fluorescence analysis.
χ < 0 → Diamagnetic (gold, silver, copper, water)
χ > 0 → Paramagnetic (aluminium, platinum, oxygen)
χ >> 0 → Ferromagnetic (iron, nickel, cobalt)
Silver and platinum in comparison
Silver (χ ≈ −2.4 × 10⁻⁵) and copper are also diamagnetic. Platinum is interesting: it is paramagnetic (χ > 0) and is minimally attracted by strong magnets — a useful distinguishing feature when testing white metals. Palladium is likewise paramagnetic. This makes the magnet test less clear-cut for platinum and palladium than for gold or silver.
| Metal | Susceptibility χ (SI) | Type |
|---|---|---|
| Gold | −3.4 × 10⁻⁵ | Diamagnetic |
| Silver | −2.4 × 10⁻⁵ | Diamagnetic |
| Copper | −9.6 × 10⁻⁶ | Diamagnetic |
| Platinum | +2.9 × 10⁻⁴ | Paramagnetic |
| Palladium | +7.9 × 10⁻⁴ | Paramagnetic |
| Iron | ~10⁵ | Ferromagnetic |
In brief
Gold is diamagnetic — it is weakly repelled by magnets, never attracted. Anyone keeping an eye on the current gold price who wants to buy genuine gold should know the magnet test as a quick first check — but always use it as a complement to more precise methods such as density testing or XRF.