Diamagnetism of Gold
Also: Diamagnet, negative magnetic susceptibility
Diamagnetism is the faint pushing-away of a material by a magnetic field; because gold is diamagnetic, magnets do not draw it in.
Gold sits firmly among the diamagnetic materials: bring it near a magnetic field and, instead of being drawn in, it is nudged away by a vanishingly small amount. The push is so faint that nothing about it registers in daily life — but it matters a great deal when it comes to the authenticity testing of gold coins and bars.
What is going on physically
When an external field is switched on, it induces tiny looping currents within an atom's electron shells. Lenz's law dictates that these currents throw up a field pointing against the applied one, so the material gets repelled. Gold's electron shells are all completely filled and hold no unpaired electrons, which means it has none of the permanent magnetic moment that paramagnetism or ferromagnetism would require. The upshot is a negative magnetic susceptibility, χ ≈ −3.4 × 10⁻⁵ (SI, dimensionless).
This diamagnetic response neither depends on temperature nor amounts to much — quite unlike paramagnetism, which obeys Curie's law, or the powerful pull of ferromagnetism seen in iron, nickel and cobalt.
Why it helps verify authenticity
Reaching for a magnet is a quick, non-destructive opening move:
- A strong neodymium magnet will not grab hold of real gold.
- A firm pull instead flags ferromagnetic contaminants or a hidden core — the giveaway of a classic tungsten forgery.
- Watch out: non-magnetic materials like brass, tungsten and lead sail through the magnet test too, so passing it does not rule a fake out.
To be sure of your result, pair the magnet test with the density test after Archimedes 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)
How silver and platinum stack up
Both silver at χ ≈ −2.4 × 10⁻⁵ and copper are diamagnetic as well. Platinum is the intriguing case: it is paramagnetic (χ > 0), so a strong magnet tugs on it ever so slightly — a genuinely useful tell when you are sorting through white metals. Palladium behaves the same way. That is what makes the magnet test more ambiguous for platinum and palladium than it is 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 |
The short version
Gold is diamagnetic — magnets repel it faintly and never attract it. If you track the current gold price with an eye to buying the real thing, keep the magnet test in mind as a fast first pass, but always treat it as a companion to sharper methods like density testing or XRF.