秋田大学大学院国際資源学研究科附属鉱業博物館 ―岩鉱分野の展示の見どころ―

Spectroscopy has been widely used in geology since the 1990s because it is non-destructive and easy to analyze. Raman spectroscopy has generally been used to identify mineral phases in geology, but recent studies have proposed new methods to quantitatively estimate the metamorphic pressure (quartz Raman barometry) and peak temperature (Raman carbonaceous material geothermometry). Studies using infrared spectroscopy are also underway to advance our understanding of hydration processes in subduction zones and mantle through the analysis of water in rocks. In addition to the development of new methods using spectroscopy, new tools are also being developed to analyze huge amounts of data through iterative processing, which will enable the extraction of more informative and quantitative results in a shorter time. This paper introduces examples of spectroscopy applications in geology and examines future developments.

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%.