Uranium is a green quartz like material that's used in making advanced units such as Arachnid, Centurion, Hellfire, Railgun tank, Masher, and Doom Walkers. A Uranium mine can be built on a Uranium patch. These patches have different levels. The higher the level the more of that resource you can mine. It is a limited resource and often hard to find and competed over. You can also earn Uranium and Titanium as rewards when you complete 'gain attack points' missions.
Uranium and titanium are commonly located close to the center between -25 X-axis, -15 Y and while they can be found further beyond that they are not as frequent as titanium.