Which two elements combine to make most of the common rock forming minerals in the crust?

Those two elements are silicon and oxygen.
Silicon and oxygen together form most of the silicates which can be found in Earth's crust. They appear on other planets too, as well as moons and asteroids. The combination of silicon and oxygen creates many types of minerals, such as olivine, pyroxene, amphiboles, quartz, etc.

Answer mauritania is in the northwestern part of african, meaning its in the western hemisphere, and how do i know/ the map showed me so; ///: )

If a particular resource is not useful or needed then the price would be considerably low. once that resource is needed the price or value will raise depending on how useful or needed it is especially if the resource is low in quantity, the consumers would pay whatever they have to, to get that material.