Asked by: Tony Moorhouse, SuttonGold is called a heavy metal because of its high density, which comes from the fact that each of its atoms is individually very heavy. The density of tungsten is almost identical, but tungsten is hard and brittle because its atoms are tightly linked and it is difficult to force them past each other. In contrast, gold atoms slide past each other relatively easily, which makes the metal soft and malleable. Gold is so soft, in fact, that one gram of it can be beaten into a sheet covering nearly a square metre. Such sheets are used in the process of 'gilding'.