用語「カリ長石」と「アルカリ長石」について

抄録

The usage of “potassium feldspar” and “alkali feldspar” has been confused in earth sciences for a long time. The term “alkali feldspar” is for the solid solution series between the two components of KAlSi₃O₈ (potassium feldspar) and NaAlSi₃O₈ (sodium feldspar), including more or less CaAl₂Si₂O₈ (lime feldspar) as the third component. The term “potassium feldspar” is in practice for KAlSi₃O₈ as an end member of the feldspar solid solution. At present, the scientific or appropriate usage of the two terms without confusion is needed in earth sciences. This review outlines the history of hitherto confused usage of the two terms, and interprets how important the appropriate usage of the two terms is in earth sciences, especially in mineralogical and petrological sciences. We recommend that perthite should be termed not “potassium feldspar” but alkali feldspar, and that the term potassium feldspar should be applied to alkali feldspar at least with KAlSi₃O₈ content ≥ 90 mol%.