A Proposal to Change “Potassium Feldspar” to “Alkali Feldspar” in Japanese Earth Science Textbooks

<p>Feldspar is a mineral family name that includes several solid solution series composed mainly of aluminosilicates. The solid solution name of potassium feldspar (or orthoclase) (KAlSi3O8:Or) - albite (NaAlSi3O8:Ab) is alkali feldspar. In the classification of igneous rocks proposed by the International Union of Geological Sciences (IUGS), “alkali feldspar” is used instead of “potassium feldspar.” On the other hand, in Japan, the solid solution name of potassium feldspar, albite, has been known as “potassium feldspar (or orthoclase)” in geology textbooks for upper secondary school students since the Heisei era (1989–), and these terms as used in textbooks have not as yet been fully examined. In this study, we investigated textbooks from the Meiji to Heisei era (from 1968 to the present) to clarify changes in the treatment of the term “potassium feldspar (or orthoclase).” From our investigations, we found that “potassium feldspar” has been conventionally used since the early Meiji Era and, with some changes, the term continues to be widely used to this day. The concept of a solid solution has been described in upper secondary school Earth Science textbooks since the early Heisei era (1989–), and the term “potassium feldspar,” ordinarily indicating the outer edge component of the solid solution, has been used in place of the mineral name “alkali feldspar,” which indicates the solid solution. To inline with conventional international usage and the classification system of IUGS, the term “alkali feldspar” should be considered to replace “potassium feldspar” in Japanese Science textbooks.</p>