![]() While the same charge, the size of K and Na differ by ~ 30 %! Separates Na-K from Na-Ca feldspars = f(T). THUS: see LIMITED Ab-An-Kspar solid solution (sometimes termed Anorthoclase or ternary feldspar) NOT: K+ - Ca++ (different size and charge) In general, a mineral structure will accept a mixture of cations if the cations have the same charge OR are about the same size. Range of feldspar compositions found in nature determined by the sizes and charges on Na, Ca, K. Stable compositional range as a function of P and T defined by nature and experiments: triangular diagram. Other cations substituting into feldspar = Ba, Sr, Eu (some Fe, etc).Ĭcompositions are simple, basic structures are relatively simple, structures of minerals with compositions intermediate between Alb and An, and Alb and Kspar are KAlSi3O8 = K-feldspar (sanidine, orthoclase, microcline) ![]() Derivation of minerals from the silica frameworks by substitution of elements for Si. ![]()
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