Elements that form ions with higher charge than the +2 found for the Mg+2 Fe+2 and Ca+2 present in the octahedral sites in mafic and ultramafic rock forming minerals and are larger in size than the tetrahedral Si4+ and Al3+ sites in silicate minerals are termed as :
MH SET - 2018, SET Exam - 2018,
Answer: A
They are the high field strength elements (HFSE).
HFSE such as Zr, Hf, Nb, Ta and Ti form small ions with high charge (+3 to +5 and more), so their ratio of charge to radius, the field strength, is high. Their charge is too great for the octahedral sites occupied by Mg2+, Fe2+ and Ca2+, and they are too big for the tetrahedral sites of Si and Al, so they behave as incompatible elements.
Large ion lithophile elements (K, Rb, Cs, Sr, Ba) are incompatible for the opposite reason: large ions with low charge. Transition metals such as Ni and Cr fit readily into octahedral sites, and heavy rare earth elements are a separate group defined by atomic number.
Please log in or register to report this question.