Field and experimental studies were performed to understand the formation conditions of the Nettetal zeolite deposit, Laach volcanic area, Germany. This deposit shows pronounced small- (cm) and large-scale (tens of meters) variations of zeolitization, despite the same phonolitic precursor glass throughout the occurrence. Zeolitization of the pyroclastic ash flow is restricted to three distinct layers that are 0.15 to 10 m thick and separated by fresh ash. The glassy matrix is altered to chabazite, phillipsite, analcime and K-feldspar in various combinations, whereas the pumice clasts are altered predominantly to chabazite. Mass changes during zeolite formation appear to be small, and Ca enrichment in chabazite and phillipsite may have occurred after their formation by cation exchange.

The zeolites and zeolite assemblages observed in the Nettetal deposit were experimentally reproduced by reacting the phonolitic glass at 100–200°C with distilled water and 0.01 M alkaline solutions as well as with varying solid/liquid ratios and grain-sizes. Chabazite and phillipsite represented metastable transition phases with respect to analcime and K-feldspar. A high solid/liquid ratio accelerated the conversion of glass to zeolites.

None of the classic models of zeolite formation is fully applicable to the Nettetal deposit. The most probable environment for zeolitization in this deposit is the stagnant fringe water zone immediately above the groundwater table. In this zone, representing a relatively closed system, favorable solution compositions for zeolite formation could have been developed rather quickly by glass-water interaction, which is not possible within the more thoroughly flushed deeper parts of the groundwater system. The three distinct zeolite layers are probably the result of temporarily changing groundwater levels.

The new sodalite-group mineral bolotinaite, ideally (Na7□)(Al6Si6O24)F⋅4H2O, was discovered in a volcanic ejectum of trachitoid sanidinite collected from the In den Dellen (Zieglowski) pumice quarry, Laach Lake (Laacher See) palaeovolcano, Eifel region, Rhineland-Palatinate, Germany. The associated minerals are sanidine, nepheline, annite and zircon. Bolotinaite occurs as isolated interpenetration prismatic twins on (111) up to 1.3 mm long, complex twins, and rare non-twinned rhombic dodecahedra up to 0.2 mm across. The colour of bolotinaite is pale yellow to pinkish coloured, the streak is white and the lustre is vitreous. Weak orange–yellow fluorescence under longwave ultraviolet radiation (λ = 330 nm) is due to the presence of trace amounts of the S2•– radical anion. Bolotinaite is brittle, with a Mohs’ hardness of 5. No cleavage is observed. The fracture is uneven. D(meas) = 2.27(2) g⋅cm–3, D(calc) = 2.291 g⋅cm–3. Bolotinaite is optically isotropic, with n = 1.488(2) (λ = 589 nm). The chemical composition is (wt.%, electron microprobe, CO2 determined by quantitative IR spectroscopy analysis, H2O calculated from the empirical formula with four H2O molecules per formula unit): Na2O 18.30, K2O 3.87, CaO 0.57, Al2O3 28.85, SiO2 37.97, CO2 1.66, SO3 1.37, F 1.60, Cl 0.57, 2.22, H2O 7.21, –O≡(F,Cl) –0.80, total 101.17. The empirical formula is (Na5.92K0.82Ca0.10H0.08)(Si6.33Al5.67O24)(SO4)0.17F0.84Cl0.16(H2O)3.96(CO2)0.38. A high content of H2O and the presence of CO2 molecules and H+ cations as well as trace amounts of S2•– are confirmed by means of infrared and Raman spectroscopy. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0335. Bolotinaite is cubic, space group I$\bar{4}$3m, with a = 9.027(1) Å, V = 735.7(2) Å3 and Z = 1. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 6.36 (47) (110), 4.502 (10) (200), 3.679 (100) (211), 2.851 (28) (310), 2.603 (29) (222) and 2.126 (18) (330). The mineral is named in honour of the Russian crystallographer and crystal chemist Dr. Nadezhda Borisovna Bolotina (b. 1949).

The new mineral stefanweissite, IMA2018-020, was discovered in sanidinite volcanic ejecta from the Laach Lake (Laacher See) paleovolcano, Eifel region, Rhineland-Palatinate, Germany. Associated minerals are sanidine, nosean, biotite, augite, titanite, ferriallanite-(La), magnetite, baddeleyite and a pyrochlore-group mineral. Stefanweissite is brown and reddish-brown, with adamantine lustre; the streak is light brown to yellow. It forms long-prismatic crystals up to 0.03 mm × 0.07 mm × 1.0 mm and acicular crystals up to 2 mm long and 0.02 mm thick typically combined in radiated aggregates in cavities in sanidinite. Dcalc. = 5.254 g/cm3. The mean refractive index calculated from the Gladstone–Dale equation is 2.260. The Raman spectrum shows the absence of hydrogen-bearing groups. The chemical composition is (electron microprobe, wt.%): CaO 7.63, MnO 2.51, FeO 7.86, Al2O3 0.25, La2O3 2.28, Ce2O3 6.54, Pr2O3 1.01, Nd2O3 1.59, ThO2 3.71, UO2 1.09, TiO2 17.32, ZrO2 28.03, HfO2 0.91, Nb2O5 19.96, total 99.69. The empirical formula based on 14 O atoms per formula unit is Ca1.13(Ce0.33La0.12Nd0.08Pr0.05)Σ0.58Th0.12U0.03Mn0.29Fe0.91Al0.04Zr1.89Hf0.04Ti1.80Nb1.19O14. The simplified formula is (Ca,REE)2Zr2(Nb,Ti)(Ti,Nb)2Fe2+O14. Stefanweissite is orthorhombic, with space group Cmca. The unit-cell parameters are: a = 7.2896(4) Å, b = 14.1435(5) Å, c = 10.1713(4) Å and V = 1048.68(7) Å3. The crystal structure was solved using single-crystal X-ray diffraction data. Stefanweissite is an analogue of zirconolite-3O with Nb dominant over Ti in one of two octahedral sites. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 2.983(100)(202), 2.897(71)(042), 1.828(38)(154, 400, 333), 1.793(25)(244), 1.767(16)(080), 1.517(10)(282), 1.187(19)(483, 1.11.3, 602). Type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, with the registration number 5191/1.

New electron-microprobe analyses of mayenite from the Ettringer Bellerberg volcano near Mayen in the Eifel district, Germany have high Cl contents and Raman spectroscopy indicates the presence of OH groups. Neither of these components is included in the generally accepted chemical formula, Ca12Al14O33. A refinement of the crystal structure by single-crystal X-ray methods reveals a previously unrecognized partial substitution. The O2 site which forms one of the apices of an AlO4 tetrahedron (with 3 × O1 sites) is replaced by 3 × O2a sites, which change the coordination of the central Al atom from tetrahedral to octahedral. This substitution is related to partial hydration of Ca12Al14O32Cl2 according to the isomorphic scheme (O2– + Cl–) ↔ 3(OH)–. The revised composition of Eifel mayenite is best described by the formula Ca12Al14O32–xCl2–x(OH)3x (x ∼0.75); the original formula, Ca12Al14O33, is inadequate. The analysed mineral can be considered to consist of endmember Ca12Al14O32Cl2 (62.5 mol.%) and endmember Ca12Al14O30(OH)6 (37.5 mol.%).

Hielscherite, ideally Ca3Si(OH)6(SO4)(SO3)·11H2O, (IMA 2011-037) is the first ettringite-group mineral with essential sulfite. We have identified a continuous natural solid-solution series from endmember thaumasite, Ca3Si(OH)6(SO4)(CO3)·12H2O, to a composition with at least 77 mol.% endmember hielscherite. In this series, the SO3:CO3 ratio is variable, whereas the SO4 content remains constant. Compositions with more than 50 mol.% endmember hielscherite have only been found at Graulay quarry near Hillesheim in the western Eifel Mountains, Rhineland-Palatinate, where they occur with phillipsite-K, chabazite-Ca and gypsum in cavities in alkaline basalt. Sulfite-rich thaumasite has been found in hydrothermal assemblages in young alkaline basalts in two volcanic regions of Germany: it is widespread at Graulay quarry and occurs at Rother Kopf, Schellkopf and Bellerberg quarries in Eifel district; it has also been found at Zeilberg quarry, Franconia, Bavaria. Hielscherite forms matted fibrous aggregates up to 1 cm across and groups of acicular to prismatic hexagonal crystals up to 0.3 × 0.3 × 1.5 mm. Individual crystals are colourless and transparent with a vitreous lustre and crystal aggregates are white with a silky lustre. The Mohs hardness is 2–2½. Measured and calculated densities are Dmeas = 1.82(3) and Dcalc = 1.79 g cm–3. Hielscherite is optically uniaxial (–), ω = 1.494(2), ε = 1.476(2). The mean chemical composition of holotype material (determined by electron microprobe for Ca, Al, Si, and S and gas chromatography for C, H and N, with the S4+:S6+ ratio from the crystal-structure data) is CaO 27.15, Al2O3 2.33, SiO2 7.04, CO2 2.71, SO2 6.40, SO3 12.91, N2O5 0.42, H2O 39.22, total 98.18 wt.%. The empirical formula on the basis of 3 Ca atoms per formula unit is Ca3(Si0.73Al0.28)Σ1.01(OH)5.71(SO4)1.00(SO3)0.62(CO3)0.38(NO3)0.05·10.63H2O. The presence of sulfite was confirmed by crystal-structure analysis and infrared and X-ray absorption near edge structure spectra. The crystal structure of sulfite-rich thaumasite from Zeilberg quarry was solved by direct methods based on single-crystal X-ray diffraction data (R1 = 0.064). The structure of hielscherite was refined using the Rietveld method (Rwp = 0.0317). Hielscherite is hexagonal, P63, a = 11.1178(2), c = 10.5381(2) Å, V = 1128.06(4) Å3 and Z = 2. The strongest reflections in the X-ray powder pattern [(d, Å (I)(hkl)] are: 9.62(100)(010,100); 5.551(50)(110); 4.616(37)(012,102); 3.823(64)(112); 3.436(25)(211), 2.742(38)(032,302), 2.528(37)(123,213), 2.180(35)(042,402;223). In both hielscherite and sulfite-rich thaumasite, pyramidal sulfite groups occupy the same site as trigonal carbonate groups, with analogous O sites, whereas tetrahedral sulfate groups occupy separate positions. Hielscherite is named in honour of the German mineral collector Klaus Hielscher (b. 1957).

Uplift of the Rhenish Massif can be demonstrated by means of the stream-made river terrace system that accompanies the Rhine river and its tributaries along their way through or within this part of the Variscan fold and thrust belt. The height difference between a former valley floor, especially that of the Younger ‘Hauptterrasse’ (Main Terrace), and the recent one allows to quantify the uplift by the amount of downcutting erosion. The uplift velocity increased just after the BRUNHES / MATUYAMA boundary, i.e. about 0.8 Ma B.R Since that time, a domal uplift of more than 250 m is documented in the eastern Hunsriick and in the south-eastern Eifel. The area of this maximum height anomaly is situated just between the East-and West-Eifel Quaternary volcanic districts. Thus, causal connections are supposed. The domai uplift is affected by normal faulting partly inherited since Tertiary rifting.