Nuclear fusion releases energy when light nuclei combine, because the product is more tightly bound than the ingredients were. This holds up to a point, and then it stops. Binding energy per nucleon rises steeply from hydrogen and reaches its practical maximum around mass 56, at iron. Beyond that point, fusing nuclei together costs energy rather than releasing it.
A massive star therefore burns through successive shells, hydrogen to helium, helium to carbon and oxygen, and onward through neon, magnesium and silicon, each stage faster than the last, until it has built an iron core. At that point there is nothing left to burn. The core has no source of pressure to hold itself up, it collapses in a fraction of a second, and the star explodes.
Every element heavier than iron anywhere in the universe was made in such an event, or in the collision of neutron stars, by neutron capture rather than by fusion, and those processes are comparatively rare. This is why iron is common and gold is not, and it is a far better explanation of gold's value than any story about its colour.
Iron is the most abundant element in the Earth taken as a whole, roughly a third of the planet's mass, because it was abundant in the material the solar system formed from and because it is dense enough to have sunk. The core is iron with some nickel, liquid on the outside and solid at the centre, and convection in that liquid iron generates the magnetic field that shields the surface from the solar wind. The habitability of the planet rests on it.