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.
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Gold belongs to the 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 holds 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. Since all electron shells of gold are completely filled and there are no unpaired electrons, the permanent magnetic moment required for paramagnetism or ferromagnetism is absent. 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 causes strong attraction.
Significance for Authenticity Testing
The magnet test is a first, fast, and non-destructive testing method:
- A powerful neodymium magnet does not attract genuine gold.
- Strong attraction indicates ferromagnetic impurities or core fillings (a classic sign of tungsten forgeries).
- Caution: Non-magnetic metals such as brass, tungsten or lead also pass the magnet test — it does not fully rule out counterfeits.
For a reliable assessment, the magnet test should always be combined with Archimedes density testing or 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. Interesting is platinum: it is paramagnetic (χ > 0) and is minimally attracted by powerful magnets — a useful distinguishing characteristic when testing white metals. Palladium is also 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 and looking 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 analysis.