Metals

is readily found on the Martian surface, deposited from ancient tectonic activity and meteor blasts. Further deposits can be found beneath the surface (by either Orbital Probes or Sensor Towers) which can be then mined with Metal Extractors.

Metal is a basic building material and is used in a wide range of buildings. It is also used for manufacturing Machine Parts.

Background
Since very early in human history, metals play a vital role in the art of creation. From simple copper tools and nails, to iron decorations to entire structures made out of steel. It would seem their role is not exhausted only on Earth, but will continue to serve as an accessible and vital resource for all our needs on Mars as well.