Actually, the reason iron is so cheap is because life chemistry and tectonic-hydrothermal processes have concentrated it. The bulk of the reserves date back from the Great Oxygenation event from 2-1 bn years ago when the first photosynthetic life oxidized the iron dissolved in the ocean and precipitated it at the bottom of the then-ocean. This didn't happen to aluminium, which is more abundant than iron, to the same extent. Aluminium was only discovered in the 19th century and only produced economically as a purified metal in the latter part of that century. Iron itself took some technology to become cheap and abundant and before the 12th century BC was regarded as a precious metal (see: <a href="https://en.wikipedia.org/wiki/Meteoric_iron" rel="nofollow">https://en.wikipedia.org/wiki/Meteoric_iron</a> ).<p>The price of metals does not match their abundance in the Earth's crust and least of which the Earth as a planet.