Differences in the interlayer between NH₄ and K micas, caused by H bonds in the former, explain forbidden mixed compositions near the K endmember. The areas of the samples with these compositions resolve their energetically unfavourable nature through the coexistence, at the nanoscale, of muscovite (and/or illite) with NH₄ micas containing varying proportions of K. For all other NH₄/K ratios, continuous solid-solution series exits as these compositions are energetically favourable.

The high-pressure behavior of benitoite was studied by synchrotron single-crystal X-ray diffraction up to 22.3 GPa. Three phase transitions were identified: benitoite → II (3.9–4.4 GPa), II → III (12.4–13.1 GPa), and III → IV (16.4–17.1 GPa). Structural evolution and deformation mechanisms are reported, highlighting Si₃O₉ ring rearrangements. These results clarify ring stabilization in silicates and offer analogues for high-pressure CaSiO₃ phases and sp³ carbonates in planetary interiors.