The Journal American Mineralogist has published in the issue of November-December an extensive review from the ICV-CSIC, in collaboration with the ICMM-CSIC and NHMFL of Florida (USA), about the order detected in K-feldspars by multinuclear NMR at high and intermediate magnetic fields, which improve our understanding of order/disorder relationships among feldspars. This study can be essential to understand the nature of the crystalline order that have not been detected by the conventional reciprocal space techniques. It shows that there exists medium-range Si-Al-K or molecular-like order (MRO) in “real crystals”, involving not only the tetrahedral sites but also the alkali cation position, which cannot be captured by standard diffraction methods, using the lattice model as “ideal crystals” from average structure solutions. These results suggest that the conventional systematic of potassium feldspars established in 1934 should be modified. In addition to the mineral species accepted by the IMA (“International Mineralogical Association”) including sanidine, orthoclase and microcline, it could be added “valencianite” as a new mineral species of the K-feldspars group.
