Elba tourmaline crystals commonly display a sharp transition to dark colors at the analogous termination, but the mechanisms leading to the formation of such terminations are unclear. Here we propose a general genetic model in which, as a consequence of a pocket rupture event, chemical alteration of early formed Fe-/Mn-rich minerals in the enclosing pegmatite was responsible for the release of Fe and/or Mn in the geochemical system, allowing the formation of the late-stage dark terminations.

Paramontroseite is a V dioxide (a = 4.8960(14) Å, b = 9.395(3) Å, c = 2.9163(5) Å, V = 134.14(6) ų; space group Pbnm). The sample under investigation (Prachovice mine, Czech Republic) bears 20 wt % of Fe₂O₃, and the Fe atoms occupy tetrahedral sites arranged in the empty channel along z. Thermal expansion is anisotropic. At T > 350 °C, paramontroseite decomposes and two new phases form: V₂O₅ (V-pentoxide) and V₄Fe₂O₁₃ (Fe-tetrapolyvanadate).

Synthetic lepidolites and Li-muscovites were characterised by nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction. Both Li and F / OH content influence the occurrence of the impurity phases. A solid solution series exists for lepidolites with polylithionite and trilithionite as endmembers but does not between trilithionite and muscovite. NMR investigations indicate there is a preference for incorporating fluorine and OH groups near Li-rich and Al-rich environments, respectively.

In this work we report a new locality for the rare mineral hydroromarchite, Sn₃O₂(OH)₂. It was found not in a submarine environment but in soil at the Saint James Church archaeological site in Creussen, Germany. A tin artefact (a tin button) was exposed to weathering in soil for about 300 years. We solved and refined its structure based on single-crystal X-ray diffraction analysis.

First occurrences of the secondary phosphate minerals kenngottite, Mn₃²⁺Fe₄³⁺(PO₄)₄(OH)₆(H₂O)₂; allanpringite, Fe₃³⁺(PO₄)₂(OH)₃·5H₂O; iangreyite, Ca₂Al₇(PO₄)₂(PO₃OH)₂(OH,F)15·8H₂O; and nizamoffite, MnZn₂(PO₄)₂(H₂O)₄, from the Hagendorf Süd pegmatite are reported, with characterisation of their crystal chemistry and phase associations.

Feldspars constitute about 60 % of the earth's crust. Na-feldspar, Na[AlSi₃O₈], is central to this mineral group. Its structural response to changing conditions of temperature and pressure is complicated. In particular, this applies to the distribution of Al and Si on the atomic sites of its crystal structure. We clarify how this distribution varies in thermodynamic equilibrium with external conditions and provide procedures that allow easy determination of the atomic distribution.