Building tall cities is made possible by the invention of concrete with steel rebar which has much more tensile strength than any other massively available material that I am aware of. Cement (the most crucial ingredient) is made by processing limestone which is an organic rock formed from corral and skeletal remains.

Rocky "earth like" planets have no limestone (or coal or oil or any other organic material) but they do have allot of basalt. What kind of materials could you manufacture from basalt? Could you make materials that have enough tensile strength to build a city?

  • $\begingroup$ Do you have a specific planet and city in mind or do you just want to build a space city and it really doesn't matter how big and where? Humans have been using basalt in certain areas for millenia. If their cities do not meet your needs: Please consider that it might be easier to simply bring the materials to build your city with you on your space ship than to do some fancy basalt stuff. Also, you might get more of an answer in a geology or construction worker forum. Gonna give you an upvote and hope someone tells me why we don't build everything from basalt. $\endgroup$ – AMT Feb 16 '17 at 12:46
  • $\begingroup$ The planet is Tau Ceti E. The city is a metropolis. $\endgroup$ – Lorry Laurence mcLarry Feb 16 '17 at 13:19
  • $\begingroup$ I would say that building tall cities is made possible by steel much more so than concrete. At least here on Earth real skyscrapers did not exist until steel allowed architects to get away from the 'massive walls carry the load of the building' paradigm. So, the premise is off. Second, the chemical reactions that limestone allows that result in the concrete curing back in to a solid just aren't going to happen with a basalt-based starting material. $\endgroup$ – Jon Custer Feb 16 '17 at 14:18
  • $\begingroup$ In that case, since the gravity is much higher on that planet - if it even exists - I wouldn't recommend building high skyscrapers. $\endgroup$ – AMT Feb 16 '17 at 15:01

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