Mineralogy and Petrology最新文献

Nickelalumite, ideally NiAl₄(SO₄)(OH)₁₂(H₂O)₃, is a newly approved mineral from the Batken region, Kyrgyzstan, where it occurs in the Kara-Tangi and Kara-Chagyr uranium deposits. It formed in a zone of hydrothermal alteration of U–V-bearing carbonaceous siliceous schists, in association with quartz, calcite, alumohydrocalcite, allophane, crandallite, kyrgyzstanite, ankinovichite and an unknown Al–OH-mineral. It occurs as aggregates of colourless to pistachio-green radiating bladed crystals from 0.05 to 0.50 mm long. It is vitreous to transparent in thin flakes, has a white streak, and shows no fluorescence under long-wave or short-wave ultraviolet light. Cleavage is perfect parallel to {001} and no parting was observed. Mohs hardness is 2, it is brittle and has a splintery fracture. The calculated mass density is 2.231 g cm^–3. In transmitted plane-polarized white light, nickelalumite is non-pleochroic, biaxial, α = 1.542(2), γ = 1.533(2), β could not be measured due to the almost negligible thickness of the flakes. EPMA chemical analysis gave Al₂O₃ 39.94, SiO₂ 0.17, SO₃ 15.20, V₂O₃ 0.29, FeO 0.15, NiO 8.00, ZnO 6.21, (H₂O)_calc. 31.87, total 101.83 wt%, H₂O was determined by crystal-structure analysis, and the empirical formula is as follows: (Ni_0.55Zn_0.39V_0.02Fe_0.01)_Σ0.97(Al_3.99Si_0.01)_Σ4.00 (SO₄)(OH)₁₂(H₂O)₃ based on 4 (Al + Si) cations. There is considerable variation in substitution of Zn, Cu, Fe and V³⁺ for Ni and V⁵⁺ for S⁶⁺. Nickelalumite is monoclinic, P2₁/n, a = 10.2567(5), b = 8.8815(4), c = 17.0989(8) Å, β = 95.548(1)°, V = 1550.3(2) ų, Z = 4. The crystal structure of nickelalumite was refined to an R₁ index of 5.66% and consists of interrupted [NiAl₄(OH)₁₂] sheets intercalated with layers of {(SO₄)₂(H₂O)₃}; nickelalumite is a member of the chalcoalumite group.

The "Snowball Earths" were cataclysmic events during the late Neoproterozoic's Cryogenian period (720-635 Ma) in which most, if not all, of Earth’s surface was covered in ice. Paleoenvironmental reconstructions of these events utilize isotopic systems, such as Δ¹⁷O and barium isotopes of barites. Other isotopic systems, such as zinc (Zn), can reflect seawater composition or environmental conditions (e.g., temperature changes) and biological productivity. We report here a multi-isotopic C, O, and Zn data set for carbonates deposited immediately after the Marinoan glaciation (635 Ma) from the Otavi Group in northern Namibia. In this study, we chemically separated calcite and non-calcitic carbonate phases, finding isotopically distinct carbon and oxygen isotopes. These could reflect changes in the source seawater composition and conditions during carbonate formation. Our key finding is largescale Zn isotopic variations over the oldest parts of the distal foreslope cap carbonate sections. The magnitude of variation is larger than any found throughout post-snowball cap carbonates to date, and in a far shorter sequence. This shows a heretofore undiscovered difficulty for Zn isotopic interpretations. The primary Zn sources are likely to be aeolian or alluvial, associated with the massive deglaciation related run-off from the thawing continent and a greater exposed surface for atmospheric aerosol entrainment. The samples with the lightest Zn isotopic compositions (δ⁶⁶Zn < 0.3 ‰) potentially reflect hydrothermally sourced Zn dominating the carbonates’ Zn budget. This finding is likely unique to the oldest carbonates, when the meltwater lid was thinnest and surface waters most prone to upwelling of hydrothermally dominated Snowball Earth brine. On the other hand, local variations could be related to bioproductivity affecting the Zn isotopic composition of the seawater. Similarly, fluctuations in sea-level could bring the depositional site below and above a redoxcline, causing isotopic variations. These variations in Zn isotope ratios preclude the estimation of a global Zn isotopic signature, potentially indicating localized resumption of export production.

Three new copper-lead selenite bromides were synthesized by chemical vapor transport reactions. Pb₅Cu⁺₄(SeO₃)₄Br₆ is monoclinic, space group C2/m, a = 17.7248(14), b = 5.5484(5), c = 12.7010(10) Å, β = 103.398(2)º, V = 1215.08(17) ų, R₁ = 0.024; Pb₈Cu²⁺(SeO₃)₄Br₁₀ is orthorhombic, space group I222, a = 9.5893(5), b = 12.4484(9), c = 12.7927(6) Å, V = 1527.08(15) ų, R₁ = 0.027; Pb₅Cu²⁺(SeO₃)₄(Br,Cl)₄ is monoclinic, C2/c, a = 24.590(6) Å, b = 5.5786(14) Å, c = 14.248(4) Å, β = 102.883(7)º, V = 1905.3(9) ų, R₁ = 0.026. The crystal structure of Pb₅Cu⁺₄(SeO₃)₄Br₆ consists of two distinct parts: corner- and edge-sharing Cu⁺Br₄ tetrahedra form infinite [Cu⁺₄Br₆]^2- layers which alternate with [Pb₅(SeO₃)₄]²⁺ layers. Pb₈Cu²⁺(SeO₃)₄Br₁₀ contains positively charged unique [Pb₈Cu²⁺(SeO₃)₄]¹⁰⁺ rod-like chains with Cu²⁺ cations in the core. These chains are held together by Br^- anions. Pb₅Cu⁺₄(SeO₃)₄Br₆ and Pb₈Cu²⁺(SeO₃)₄Br₁₀ belong to new structure types. Pb₅Cu²⁺(SeO₃)₄(Br,Cl)₄ is a synthetic analogue of the mineral sarrabusite, Pb₅Cu(SeO₃)₄Cl₄, previously known from an electron diffraction study. The investigation of this synthetic equivalent of sarrabusite by conventional single-crystal X-ray diffraction provides a distinctly improved insight in this crystal structure. Cu atom has well-defined [2O+(2O+2X)] (X = halogen) distorted octahedral coordination. PbO_n and SeO₃ polyhedra interconnect via common oxygen atoms into [Pb₅(SeO₃)₄]²⁺ layers parallel to (001). Cu²⁺ cations interconnect the layers into the framework with the large cavities filled by halide X anions. In all three new compounds described, a common feature is the formation of the selenophile substructure which is terminated by a ‘lone-pair’ shell that faces bromide complexes thus forming the surface of a halophile substructure.

A second study of ferriallanite-(Ce) from Nya Bastnäs, Sweden, extends current data by using electron probe micro-analysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis and brings new insights about its crystal chemistry obtained by Raman spectroscopy. The study presents the first Raman spectra for ferriallanite-(Ce) member of the allanite group (not considering the rather low-quality spectra published in preceding papers). The material does not show significant radiation damage, which is rare as allanite-group minerals often have undergone metamictisation due to significant amounts of incorporated radionuclides (U, Th). Some interior regions show pronounced zoning that correlates with variations in Raman-band positions. In spite of its significant REE content, the material is virtually non-luminescent. New additional data for allanite-(Ce) from Oßling, Germany and Domanínek, Czech Republic are also presented, which were used for comparison.

The microporous crystal structure of zemannite, Mg(H₂O)₆[Zn²⁺Fe³⁺(TeO₃)₃]₂·nH₂O, n ≤ 3, was re-investigated based on single-crystal X-ray diffraction data measured at 298 ± 0.5 K, 200 ± 1 K and 100 ± 3 K. So far, zemannite was described in space group P6₃ exhibiting a pronounced pseudosymmetry (P6₃/m). All refinements confirm the [Zn²⁺Fe³⁺(TeO₃)₃]¹⁻ framework topology with the extra-framework constituents (Mg atoms and H₂O molecules) being located within the channels along [001]. Measurements on a sample from the type locality revealed the unexpected occurrence of 00l reflections with l = 2n + 1, which clearly violate the 6₃ screw-axis symmetry. The minor but significant intensities of the low-order 00l reflections are assigned to the small differences in the scattering power between the Fe and Zn atoms; thus, the Zn and Fe cations are partly ordered between crystallographically distinct sites within the framework. In addition, the low symmetry allows a full order of the extra-framework atoms for the first time. A series of comparative refinement models were performed in the space groups P6₃/m, P6₃, P(overline{6}), and P3. A fully ordered arrangement of the extra-framework guest atoms confirms the earlier postulated theoretical structure model with a hexahydrated Mg²⁺ ion besides additional interstitial H₂O molecules. The final refinements in space group P3 yield R1 ≤ 0.025 for the entire data sets measured at the distinct temperatures (2θ_max = 101.4°, MoKα radiation). The polarity of the arrangement in the channels is restricted to individual domains of equal twin fractions related by a mirror plane parallel to (0001).

Three ammonium-iron-sulfites (AIS) from a burning coal dump in an abandoned open coal pit at Pécs-Vasas (Mecsek Mountains, South Hungary) were identified: (NH₄)₉Fe³⁺(SO₃)₆ (AIS-1), (NH₄)₂Fe²⁺(SO₃)₂ (AIS-2), and (NH₄)₂Fe³⁺(OH)(SO₃)₂·H₂O (AIS-3). They were formed by the interaction of decomposing iron sulfides and ammonia released from organic matter. AIS-1 and AIS-2 are metastable; they break down in a few weeks (AIS-1) respectively years (AIS-2). AIS-1 forms red, stubby columnar to thick tabular crystals up to 0.2 mm in length. AIS-2 appears as brown tabular to short prismatic crystals up to 0.1 mm, often they create columnar intergrowths. AIS-3 is more stable. It was approved as a new mineral species (mineral name kollerite, IMA-CNMNC 2018–131). Sprays of natural kollerite up to 1.5 mm are composed of yellow, long-prismatic or lath-like crystals up to 0.1 mm in length. AIS-1 is characterized by powder-X-ray diffraction only. The crystal structures of AIS-2 [synthetic material, R(overline {3})m, a = 5.3879(8), c = 19.980(4) Å] and kollerite [Cmcm, a = 17.803(15), b = 7.395(5), c = 7.096(5) Å] were investigated by single-crystal X-ray diffraction. AIS-2 is topologically equivalent to bütschliite. Isolated Fe²⁺O₆ polyhedra are corner-connected to sulfite anions. 2D nets with composition [Fe²⁺(SO₃)₂]²⁻ are parallel to (0001). Kollerite crystallizes in a new structure type. The FeO₆ octahedra are corner linked to buckled [Fe³⁺(OH)(SO₃)₂]²⁻ chains. In both cases, ammonium cations are intercalated. Connection is verified by hydrogen bonds only; all H atom positions are located experimentally.

Abstract

Kobellite is a Pb-Bi-Sb sulfosalt with minor amounts of (Cu, Fe) and with the crystal structure composed of two types of rods, one of which has unusual lateral extensions (‘lobes’), which depart from the usual lozenge-shaped rod cross-section in sulfosalts. Several Pb-Bi-Sb and Pb-Sb-rich sulfosalts form a small group built on similar principles. Some of them are related by homology (e.g., izoklakeite), and differ by the perpendicular dimensions of rods (length and multiplicity of atomic layers in a rod; e.g., sterryite), and especially by different combinations of archetypes and archetype portions which participate in the rods (PbS archetype and the two orientations of SnS archetype). The present article summarizes and discusses the published data on the group. Homeotypism makes the group interesting and potentially a fertile source of further structural varieties.