Zinkgruvanite, Ba₄Mn²⁺₄Fe³⁺₂(Si₂O₇)₂(SO₄)₂O₂(OH)₂, a new ericssonite-group mineral from the Zinkgruvan Zn-Pb-Ag-Cu deposit, Askersund, Örebro County, Sweden

Zinkgruvanite, ideally Ba4Mn42+Fe23+(Si2O7)2(SO4)2O2(OH)2, is a new member of the ericssonite group, found in Ba-rich drill core samples from a sphalerite- and galena- and diopside-rich metatuffite succession from the Zinkgruvan mine, Örebro County, Sweden. Zinkgruvanite is associated with massive baryte, barytocalcite, diopside and minor witherite, cerchiaraite-Al, and sulfide minerals. It occurs as subhedral to euhedral flattened and elongated crystals up to 4 mm. It is almost black and semi-opaque with a dark-brown streak. The lustre is vitreous to sub-adamantine on crystal faces and resinous on fractures. The mineral is brittle with an uneven fracture. VHN100=539, and HMohs ≈ 4.5. In thin fragments, it is reddish-black, translucent and optically biaxial (+), 2Vz > 70∘. Pleochroism is strong and deep brown-red (E ⊥ {001} cleavage) to olive-pale-brown. Chemical point analyses by WDS-EPMA (wavelength-dispersive X-ray spectroscopy electron probe microanalyser) together with iron valencies determined from Mössbauer spectroscopy yielded the empirical formula (based on 26 O+OH+F+Cl anions): (Ba4.02Na0.03)Σ4.05(Mn1.79Fe1.562+Fe0.423+Mg0.14Ca0.10Ni0.01Zn0.01)Σ4.03(Fe1.743+Ti0.20Al0.06)Σ2.00Si4(S1.61Si0.32P0.07)Σ1.99O24(OH1.63Cl0.29F0.08)Σ2.00. The mineral is triclinic, in space group P1¯, with unit-cell parameters a=5.3982(1) Å, b=7.0237(1) Å, c=14.8108(4) Å, α= 98.256(2)∘, β= 93.379(2)∘, γ= 89.985(2)∘ and V= 554.75(2) Å3 for Z=1. The eight strongest X-ray powder diffraction lines are the following (d Å (I %; hkl)): 3.508 (70; 103), 2.980(70; 114‾), 2.814 (68; 12‾2), 2.777 (70; 121), 2.699 (714; 200), 2.680 (68; 201‾), 2.125 (100; 124, 204) and 2.107 (96; 2‾21). The crystal structure (R1=0.0379 for 3204 reflections) is an array of TS (titanium silicate) blocks alternating with intermediate blocks. The TS blocks consist of HOH sheets (H for heteropolyhedral and O for octahedral) parallel to (001). In the O sheet, the Mn2+-dominant MO(1,2,3) sites give ideally Mn42+ pfu (per formula unit). In the H sheet, the Fe3+-dominant MH sites and AP(1) sites give ideally Fe23+Ba2 pfu. In the intermediate block, SO4 oxyanions and 11 coordinated Ba atoms give ideally 2× SO4Ba pfu. Zinkgruvanite is related to ericssonite and ferroericssonite in having the same topology and type of linkage of layers in the TS block. Zinkgruvanite is also closely compositionally related to yoshimuraite, Ba4Mn4Ti2(Si2O7)2(PO4)2O2(OH)2, via the coupled heterovalent substitution 2 Ti4++ 2 (PO4)3-→2 Fe3++ 2 (SO4)2− but presents a different type of linkage. The new mineral probably formed during a late stage of regional metamorphism of a Ba-enriched, syngenetic protolith, involving locally generated oxidized fluids of high salinity.

Petrochronology of Monazite-Bearing Garnet Micaschists as a Tool to Decipher the Metamorphic Evolution of the Alpine Basement

Garnet-bearing metapelites in the Helvetic and Austroalpine pre-Mesozoic polymetamorphic basement are characterised by pressure-temperature path segments reconstructed by microstructurally controlled geothermobarometry, and the Th-U-Pb monazite age distribution pattern revealed by the electron probe microanalyser (EPMA). In the Helvetic Aiguilles Rouges Massif and the Austroalpine Oetztal-Stubai basement to the NW an Ordovician-to-Silurian high temperature event preceded a pressure-dominated Carboniferous metamorphism. In the Austroalpine basement units to the south of the Tauern Window, the maximal pressures of the Carboniferous amphibolite-facies metamorphism range from 12 to 6 kbar. The decompressional P-T path segments signal a transition to low pressure conditions. A subsequent high pressure overprint is restricted to the Prijakt Subgroup unit in the Schobergruppe and documented by Cretaceous monazite crystallisation at 88 ± 6 Ma. In the Austroalpine Saualpe basement to the SE, a distinct early Permian metamorphism which started at low pressures of ~4 kbar/500 °C and reached maximal 6 kbar/600–650 °C predated the intrusion of Permian pegmatites. Permian monazite crystallised in line with the intrusion of pegmatites. Corona microstructures around the Permian monazites indicate retrogression previous to a Cretaceous high pressure metamorphism. That way, pressure-temperature-time paths resolve the spatial and temporal evolution in the polymetamorphic Alpine basement prior to the Tertiary collision.

Quantification of Trace-Level Silicon Doping in Al x Ga1–xN Films Using Wavelength-Dispersive X-Ray Microanalysis

Wavelength-dispersive X-ray (WDX) spectroscopy was used to measure silicon atom concentrations in the range 35–100 ppm [corresponding to (3–9) × 1018 cm−3] in doped Al x Ga1–xN films using an electron probe microanalyser also equipped with a cathodoluminescence (CL) spectrometer. Doping with Si is the usual way to produce the n-type conducting layers that are critical in GaN- and Al x Ga1–xN-based devices such as LEDs and laser diodes. Previously, we have shown excellent agreement for Mg dopant concentrations in p-GaN measured by WDX with values from the more widely used technique of secondary ion mass spectrometry (SIMS). However, a discrepancy between these methods has been reported when quantifying the n-type dopant, silicon. We identify the cause of discrepancy as inherent sample contamination and propose a way to correct this using a calibration relation. This new approach, using a method combining data derived from SIMS measurements on both GaN and Al x Ga1–xN samples, provides the means to measure the Si content in these samples with account taken of variations in the ZAF corrections. This method presents a cost-effective and time-saving way to measure the Si doping and can also benefit from simultaneously measuring other signals, such as CL and electron channeling contrast imaging.

First Occurrence of Willhendersonite in the Lessini Mounts, Northern Italy

Willhendersonite is a rare zeolite, with very few occurrences reported globally (Terni Province, Italy; the Eifel Region, Germany; Styria, Austria). Moreover, the data available from these sites are very limited and do not allow a detailed picture of this zeolite’s mineralogical and chemical characteristics. In this work, a new willhendersonite occurrence is reported from the Tertiary volcanic rocks of the Lessini Mounts, northern Italy. Morphology, mineralogy and chemical composition of selected crystals were studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray Diffraction (XRD), and electron probe microanalyser (EPMA). Willhendersonite occurs within basanitic rocks as isolated, colorless, transparent crystals with prismatic to flattened morphologies. Individual crystals often grow together to form small elongated clusters and trellis-like aggregates. The diffraction pattern exhibits 33 well-resolved diffraction peaks, all of which can be indexed to a triclinic cell with unit cell parameters a = 9.239(2) Å; b = 9.221(2) Å; and c = 9.496(2) Å, α = 92.324(2)°, β = 92.677(2)°, γ = 89.992° (Space Group P1¯). The chemical data point to significant variability from Ca-rich willhendersonite (K0.23Na0.03)Σ=0,26Ca1.24 (Si3.06Al3,00Fe3+0.01)Σ=6,07 O12·5H2O) to Ca-K terms (K0.94Na0.01)Σ=0,95Ca0.99 (Si3.07Al2.93Fe3+0.00)Σ=6,00O12·5H2O). Willhendersonite from the Lessini Mounts highlights the existence of an isomorphous series between the Ca-pure crystals and Ca-K compositions, possibly extended up to a potassic end-member.

Negotiating a colonial Maya identity: metal ornaments from Tipu, Belize

Archaeologists recovered Colonial-period metal ornaments from Tipu, Belize, the site of a Maya occupation from 300 BC to AD 1707. This project asks to what extent the technological attributes of these ornaments reflect Mesoamerican or European influences. Investigators used microanalytical techniques, such as metallography, energy dispersive X-ray fluorescence (ED-XRF), electron probe microanalyser with energy dispersive spectroscopy (EPMA-EDS) and wavelength dispersive spectroscopy (EPMA-WDS) and surface etching, to study compositions and microstructures of the metals. Comparison of these data with technological and stylistic information of metals from other pre-Columbian and Contact-period sites reveals a confluence of indigenous and European metallurgy. Whereas the needle and bell forms and the suite of copper and bronze compositions align with indigenous metallurgical practices, the existence of lacetags and the use of brass reflect European technology. The presence of metal ornaments in association with Maya individuals in burials suggests that the Maya at Tipu were constructing and expressing new colonial identities through material markers.