Gold

At 19,300 kg/m³ a one-litre carton of gold weighs 19 kg, which is why film props are always obviously fake — nobody carries a real gold bar one-handed. Pure gold is too soft to wear, so jewellery is alloyed: 18 carat is 75% gold, 9 carat is 37.5%, and the balance changes both the colour and the density. It is the only common metal that does not tarnish at all, which is the real reason it plates electrical contacts rather than cheaper, more conductive silver.

Properties

Density

19,300 kg/m³ — 19.30 g/cm³

Melting point

1,064.2 °C

Tensile strength

120–220 MPa

Young's modulus

79 GPa

Thermal conductivity

318 W/(m·K)

Thermal expansion

14.2 µm/(m·K)

Floats in water

No

Magnetic

No

What it is used for

• Jewellery and bullion
• Connector and contact plating
• Semiconductor bond wire
• Spacecraft thermal blankets and visor coatings

How it compares

Does it rust?

Gold does not corrode in air or water. That chemical inertness is much of why it has been used for coinage and contacts for millennia.

Is it magnetic?

Gold is not ferromagnetic. It is often assumed to be because it is a metal, but most metals are not — only iron, nickel, cobalt and a few alloys are attracted to an ordinary magnet.