ИСТИНА

The crystal structure of two rare iron-containing minerals will be discussed. They contain chemically different anionic groups. Iron, besides occurring in nature in two different oxidation states, has an intermediate ionic radius with respect to other cations. For this reason iron is easily allowed to enter a wide number of different structures, and it can be coupled with many other cations with larger and smaller ionic radii. In the crystal structures being described here, we will see how iron-centered polyhedra can link with cations as different in size as REE’s and calcium, on one side, and carbon, on the other side.