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The design and formation of van der Waals (vdW) heterostructures with different two-dimensional (2D) materials provide an opportunity to create materials with extraordinary physical properties tailored toward specific applications. Mechanical exfoliation of natural vdW materials has been recognized as an effective way for producing high-quality ultrathin vdW heterostructures. Abramovite is one of such naturally occurring vdW materials, where the superlattice is composed of alternating Pb2BiS3 and SnInS4 2D material lattices. The forced commensuration between the two incommensurate constituent 2D material lattices induces in-plane structural anisotropy in the formed vdW heterostructure of abramovite, even though the individual 2D material lattices are isotropic in nature. Here, we show that ultrathin layers of vdW heterostructures of abramovite can be achieved by mechanical exfoliation of the natural mineral. Furthermore, the structural anisotropy induced highly anisotropic vibrational and optical responses of abramovite thin flakes are demonstrated by angle-resolved polarized Raman scattering, linear dichroism, and polarization-dependent third-harmonic generation. Our results not only establish abramovite as a promising natural vdW material with tailored linear and nonlinear optical properties for building future anisotropic integrated photonic devices, but also provide a deeper understanding of the origin of structural, vibrational and optical anisotropy in vdW heterostructures. [ABSTRACT FROM AUTHOR]

This paper describes specific features of isomorphism of unusual amphiboles containing up to 23 wt% ZnO and up to 1.3 wt% CuO from sulfide-free metasomatic rocks of the "Mixed Series" metamorphic complex, Pelagonian Massif, Republic of North Macedonia, in which chalcophile elements (Pb, Cu, Zn, Sb, As) occur in high concentrations in the form of oxides and oxysalts. The studied amphiboles belong to six mineral species: magnesio-riebeckite, ferri-winchite, F-dominant analogue of ferri-winchite ("ferri-fluoro-winchite"), ferri-barroisite, ferri-nybøite, and a zinc-rich amphibole related to clino-suenoite. The main substitution schemes are Zn → Mg and Na + Fe3+ → Ca + Mg. The amphibole related to clino-suenoite has been studied in the most detailed way. Its empirical formula is (Mg2.99Zn2.47Mn1.26Fe3+0.30Ca0.07)Σ7.09(Si7.89Fe3+0.06Al0.05O22)(OH)2, and it is the most Zn-rich amphibole among those that have ever been described in literary sources. This amphibole is characterized by single-crystal and powder X-ray diffraction, IR spectroscopic and optical data. The role of high barium activity in the formation of sulfide-free ores of chalcophile elements has been substantiated. A possible mechanism of sulfur immobilization can be described by the scheme S2− + 2O2 ↔ SO42−; SO42− + Ba2+ → BaSO4↓. [ABSTRACT FROM AUTHOR]

Unusual agpaitic syenites containing up to 25 vol.% lamprophyllite-group minerals (lamprophyllite, fluorlamprophyllite, barytolamprophyllite, and the new mineral species fluorbarytolamprophyllite, IMA 2016–089) have been discovered in the Niva intrusion and Mokhnatye Roga alkaline dyke belonging to the Kola Alkaline Province, northwestern Russia. The other main components of the rocks are potassium feldspar, Ti-rich aegirine-augite, aenigmatite, alkaline amphiboles, astrophyllite, natrolite, and ferripyrophyllite. Three generations of lamprophyllite-group minerals can be distinguished based on their morphological features. The new mineral fluorbarytolamprophyllite is the F-dominant analogue of barytolamprophyllite and the Ba-dominant analogue of fluorlamprophyllite. It represents the early generation of lamprophyllite-group minerals (LGM) and forms brown prismatic crystals, their radial aggregates and marginal zones of fluorlamprophyllite crystals. The lustre of the new mineral is vitreous to pearly. Mohs hardness is 2.5. Dcalc is 3.662 g/cm3. The mineral is optically biaxial (+), α = 1.738(3), β = 1.745(4), γ = 1.777(4) (589 nm), 2 V (meas.) = 55(5)°, 2 V (calc.) = 51°. The chemical composition (electron microprobe, water determined by TGA, wt.%) is: Na2O 10.01, K2O 2.65, MgO 0.43, CaO 0.64, SrO 5.59, BaO 16.23, MnO 0.50, FeO 4.44, Al2O3 0.08, TiO2 27.31, ZrO2 0.22, Nb2O5 0.91, Ta2O5 0.15, SiO2 29.35, F 2.41, H2O 0.26, total 101.18. The empirical formula based on 18 anions is (Ba0.865Sr0.44K0.46Na0.26)Σ2.025(Na2.38Ca0.09Fe0.47Mn0.06)Σ3.00(Ti2.79Mg0.09Fe0.035Nb0.06Zr0.015Ta0.01)Σ3.00(Si3.99Al0.01)Σ4.00 O16[F1.04O0.72(OH)0.24]Σ2.00. The IR spectrum is given. The strongest lines of the powder X-ray diffraction pattern are [d, Å (I,%) (hkl)]: 9.692 (40) (200), 3.726 (59) (−311), 3.414 (67) (311), 3.230 (96) (300), 3.013 (53) (−5–11), 2.780 (100) (221), 2.662 (52) (002). The crystal structure has been solved and refined to R1 = 5.07 based on 2897 independent reflections with I > 2σ(I). Fluorbarytolamprophyllite is monoclinic, space group C2/m. The unit-cell parameters refined from the powder data are: a = 19.520(5), b = 7.0995(17), c = 5.3896(20) Å, β = 96.657(23)°; V = 741.86(24) Å3, Z = 2. At Niva and Mokhnatye Roga, most of the LGM were formed during magmatic stage of syenite crystallization from alkaline melt enriched in Na, K, Ba, Fe, Ti and F. Compositional variation of the examined LGM and their textural relations show changes in the Sr/Ba ratio in the parental melt and increasing activity of F and Ba in derivatives fluids as the main factors driving this variation. [ABSTRACT FROM AUTHOR]

The new mineral kruijenite, ideally Ca4Al4(SO4)F2(OH)16·2H2O, was found in a calcic xenolith from tephra of the Feuerberg paleovolcano situated near Daun, Eifel paleovolcanic region, Rhineland-Palatinate, Germany. It is associated with fluorite, calcite, aragonite, cuspidine, magnesioferrite, hematite, sharyginite, harmunite, and an insufficiently investigated hydrous Ca-Mg-Al silicate. Kruijenite occurs as pale greenish-yellow to colourless long prismatic tetragonal crystals up to 0.1 mm × 1 mm in cavities typically combined in radiating or random aggregates. The mineral is brittle, with Mohs' hardness of 3; Dcalc is 2.573 g/cm3. The IR spectrum is given. Kruijenite is optically uniaxial (−), ω = 1.576(3), ε = 1.561(3). The chemical composition (wavelength dispersive spectrometer Oxford INCA Wave 700 EPMA analyser, H2O calculated from structural data) is: CaO 32.38 wt%, Al2O3 27.75 wt%, Cr2O3 1.45 wt%, SO3 8.09 wt%, F 5.84 wt%, H2O 25.64 wt%, -O=F -2.46 wt%, total 98.69 wt%. The empirical formula is Ca4.00(Al3.77Cr0.13)Σ3.90(SO4)0.70F2.13(OH)16.17·1.79H2O (Z = 2). Kruijenite is tetragonal, space group P4/ncc, a = 12.9299(4) Å, c = 5.2791(3) Å, V = 882.57(6) Å3, Z = 2. The crystal structure was solved and refined to R = 0.121. Kruijenite represents a novel structure type. Its structure is based on the microporous pseudo-framework built by Al(OH)6 octahedra and CaF2(OH)6 polyhedra. The strongest reflections of the powder X-ray diffraction pattern [d (I) (hkl)] are: 9.12 Å (77%) (110), 4.565 Å (100%) (220), 4.084 Å (50%) (310), 2.964 Å (74%) (321), 2.694 Å (27%) (411), 2.321 Å (24%) (431), 2.284 Å (29%) (511), 2.217 Å (22%) (321, 530), 1.971 Å (40%) (611). The mineral is named in honor of the Dutch collector of Eifel minerals Fred Kruijen (born in 1956). [ABSTRACT FROM AUTHOR]

The new zeolite martinandresite, ideally Ba2(Al4Si12O32)·10H2O, was discovered in the armenite locality of Wasenalp near the Isenwegg peak, Ganter valley, Simplon region, Switzerland. The associated minerals are armenite, quartz, dickite, and chlorite. Martinandresite forms tan-coloured blocky crystals up to 8 × 5 × 3.5 mm, their aggregates up to 6 cm across, as well as cruciform twins up to 3.5 mm. The major form is {010}; the subordinate forms are {100} and {001}. Indistinct cleavage is observed, presumably on (010) and in a direction across (010). The Mohs’ hardness is 4½. Density measured by flotation in heavy liquids is 2.482(5) g/cm3. Density calculated using the empirical formula is equal to 2.495 g/cm3. Martinandresite is optically biaxial, negative, α = 1.500(2), β = 1.512(2), γ = 1.515(2) (λ = 589 nm). 2V (meas.) = 55(10)°. The IR spectrum is given. The chemical composition of martinandresite is (wt%; electron microprobe, H2O determined by the modified Penfield method): Na2O 0.37, K2O 0.12, BaO 21.55, Al2O3 15.03, SiO2 49.86, H2O 12.57, total 99.50. The empirical formula based on 16 atoms Si + Al pfu is Na0.17K0.04Ba2.00(Al4.19Si11.81O32)H19.85O9.93. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is orthorhombic, space group Pmmn, with a = 9.4640(5), b = 14.2288(6), c = 6.9940(4) Å, V = 941.82(8) Å3 and Z = 1. The crystal structure of martinandresite is unique and is based on the Al-Si-O tetrahedral framework containing four-, six- and eight-membered rings of tetrahedra. Si and Al are disordered between the two independent tetrahedral sites. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 6.98 (74) (001), 6.26 (83) (011), 5.61 (100) (101), 3.933 (60) (220, 031), 3.191 (50) (112), 3.170 (62) (041), 3.005 (79) (231, 141). Martinandresite is named after Martin Andres (b. 1965), the discoverer of the armenite locality of Wasenalp. [ABSTRACT FROM AUTHOR]