User blog comment:Unownshipper/Metallurgists Wanted: Rapture's Natural Resources/@comment-3967731-20140812061641/@comment-75.36.136.107-20140812102016

Its the purity of the materials (to minimize expensive pre-processing them) which is important (theres probably alot of aluminum in the dirt in your backyard, but it takes a huge amount of chemical and heat processing to turn it into near pure elemental aluminum - or any of the other materials you name)

Yes you can do it to dirt but its a heck of alot easier to mass produce it from good bauxite (which is found in limited places). We may just be stuck doing inefficient processes and assume the cheap abundant geothermal energy would make a reasonable amount of production possible.

The area where Rapture is located is near the spreading point between tectonic plates so is pretty young geologically and no so likely to have much sedimentary accumulation (have to go a distance to fetch those kinds of materials)

Add also to your list the energy used to make cement (which we have covered if hephestus complex is as big as the outside views show). Similarly metalic aluminum wasnt easily possible until mass electric power was available (they actually made royalty crowns out of it and used it in place of gold because it was so rare around 1860)