This figure categorizes cations across an important part of the periodic table according to their behavior in the crystallization of magmas. Compatible ions enter early-forming phases, and they concide with ions that are concentrated in soils (as seen on the Earth Scientist's Periodic Table of the Elements and Their Ions). Large-ion lithophile elements enter late-forming phases because they make weak bonds with O2-; they are elements leached from soils and abundant in sawater (again as seen on the Earth Scientist's Periodic Table of the Elements and Their Ions). Incompatible ions enter-late forming phases in igneous rocks, and they in part coincide with the high-ioinic-potential cations that are leached from soils and are found in seawater. Some ions are incompatible because of the patters of substitution shown by Accompanying Figure 8.

          Note that some ions are more of less compatible than others. Na+, for example, enters plagioclase, but only at lower temperatures than Ca2+, because Na+ is farther from the "fairway" of intermediate ionic potential (roughly z/r = 5). On the other side of this figure, Si4+ likewise becomes more abundant than Al3+ in plagioclase at lower temperatures. That's consistent with the general greater abundance of Si4+ in igneous phases at lower temperatures, as seen in Accompanying Figure 10. If a compatible ion is one that enters early-forming igneous phases, then Si4+ is at best a borderline igneous phase. That seems like a paradox - Si4+ is an incompatible ion in crystallization of silicate magmas? - until one sees the borderline position of Si4+ on this figure and in general on the Earth Scientist's Periodic Table of the Elements and Their Ions.

  Image of a portion of the periodic table

   
  Back to the main page for the Earth Scientist's Periodic Table of the Elements and Their Ions.