The Usambara effect, i.e. a change of tourmaline colour from deep-green to dark-red with increasing path length of light, has been studied by optical absorption spectroscopy and colourimetric calculations on a sample of Tanzanian tourmaline of predominant dravite composition with 0.12 apfu Cr. For comparison a dark-green vanadium-bearing tourmaline from Tanzania (0.05 apfu V), which does not show such an effect, was also investigated. As established, the Usambara effect, by its nature, is closely related to the alexandrite effect, although in this case the colour change is not caused by change of spectral composition of the light of illumination, but by spectral positions of the spin-allowed absorption bands of Cr3+, a specific ratio of light transmission in two windows of transparency, green and red, and by non-linear, exponential dependence of the light transmittance on the thickness of sample. A threshold chromium content must be exceeded for the Usambara effect to show, that is, sufficient chromium for there to be two deep and well-demarcated windows of transparency in the visible range. The overall colouration results from mixing of two additive colours coming through the windows of transparency. A dark-green chromium-bearing tourmaline from the Ural Mountains (0.40 and 0.20 apfu Cr and Fe, respectively) shows how admixtures of other chromophore ions, namely, Fe2+ and Fe3+, can suppress the Usambara effect in tourmaline.

The crystal chemistry of allactite from Långban, Värmland (Sweden) was investigated by single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and electron microprobe analysis by wavelength-dispersive spectroscopy (EPMA-WDS). The optical spectra indicate the presence of Mn in valence state 2+ only. Assuming 16 O atoms per formula unit, arsenic as As5+ and the (OH) content calculated by charge balance, the resulting formula based on the EPMA-WDS data is (Mn2+6.73Ca0.13Mg0.12Zn0.02)∑7.00(As5+)2.00O16H8, very close to the ideal composition Mn7(AsO4)2(OH)8. In the unpolarized FTIR spectrum of allactite, fundamental (OH)-stretching bands are observed at 3236, 3288, 3387, 3446, 3484, 3562 and 3570 cm–1, suggesting that a number of OH environments, with different hydrogen bond strengths, occur in the structure. The neutron structure refinement shows that four independent H sites occur in allactite with full site occupancy, all as members of hydroxyl groups. The complex hydrogen-bonding scheme in the allactite structure is now well defined, with at least nine hydrogen bonds energetically favourable with mono-, bi- and trifurcated configurations.

Berezanskite, ideally Ti□2KLi3(Si12O30), is hexagonal, space group P6/mcc, a = 9.898(4), c = 14.276(6) Å, V = 1211.2(9) Å3, Z = 2. The crystal structure was refined to an R1 index of 2.08% based on 392 unique observed reflections. Berezanskite is isostructural with milarite, ideally ACa2BoCKT(2)(Be2Al)(T(1)Si12O30)(H2O)0–2. The structural unit is of the form [T(2)3T(1)12O30] with T(1) = Si and T(2) = Li, in which (LiO4) tetrahedra link [Si12O30] six-membered double-rings into a framework. The A, B and C sites occur in the interstices of the framework with the following site populations: A = Ti4+2, <A–O>= 1.938(2) Å; B =□2; C = K, <C–O> = 3.058(2) Å. In the T(2) = Li3 milarite-group minerals, the <C–O> distance is inversely related to the occupancy of the B site.

An unworked quartz vein-hosted gold deposit occurs in the Clew bay area of County Mayo, western Ireland. The veins are late-Caledonian in age and transect greenschist-facies poly-deformed Silurian quartzites. The veins contain disseminated arsenopyrite that may be a primary mineral source for elevated levels of arsenic (As) found in groundwater samples recovered from wells related spatially to the gold deposit. Levels from 5 to 188 μg/L (significantly above the 7.5 μg/L threshold for safe drinking water) have been detected. A series of element distribution maps using a scanning electron microscope (Hitachi model S-4700) linked to an energy-dispersive spectrometer (INCA® Oxford Instruments) and mineral distribution maps generated by QEMSCAN® (Quantitative Evaluation of Minerals by Scanning electron microscopy) were used to map the distribution of the primary arsenopyrite and related secondary As-bearing phases. Laser Raman microspectroscopy was used to identify the secondary As-bearing phases. 'Island weathering' of primary arsenopyrite together with hydrated pseudomorphs of arseniosiderite, pharmacosiderite and scorodite after arsenopyrite are recorded. Circulating groundwater hydrates the primary arsenopyrite, providing the release mechanism that forms the secondary As-bearing phases that occur as microfracture infills together with muscovite and biotite. The textural relationships between the primary and secondary As minerals indicate their potential as mineral sources of As that could enter transport pathways leading to its release into groundwater.

The Outer Layered Suite of the Cuillin Igneous Complex (Isle of Skye, NW Scotland) comprises a Peridotite Series and a younger Allivalite Series (the latter comprising troctolites, eucrites and gabbros). Close to the junction between the Peridotite and the Allivalite Series (but wholly contained within the latter), an ultramafic breccia unit containing abundant peridotite xenoliths crops out. In the Peridotite Series, reddish-brown Cr-bearing spinels are present as disseminated crystals in the peridotite and also as chromitite seams, while in the peridotite xenoliths of the breccia unit, green pleonaste occurs in both of these modes of textural occurrence. Optical absorption spectroscopy reveals that the colour difference between the two spinel phases is related mainly to variable Al, Cr and Fe contents, while crystal structural analysis shows that the cooling rate calculated utilizing the oxygen positional parameter is comparable for all samples. The intracrystalline closure temperature for the Cr-spinel in the Peridotite Series is different for the disseminated and seam textural occurrences of the spinels, while the temperatures yielded by pleonaste in the peridotite xenoliths are the same for both textural occurrences. Our dataset suggests that the pleonaste in the peridotite xenoliths has been heated and equilibrated under subsolidus conditions, probably during breccia formation. During this heating, homogenization of the closure temperatures of pleonaste spinels occurred.

Stalagmites and stalactites, as observed within natural caves, may develop inside geological repositories during constructional and post-operational periods. It is therefore important to understand actinide sorption within such materials. Towards this, experimental studies were carried out with 233U, 238Np (VI), 238Np (IV), 239Pu and 241Am radiotracers using natural speleothem samples collected from the Dharamjali cave of the Kumaon Lesser Himalayas, India. Petrological/mineralogical studies showed that natural speleothems have three general domains: (1) columnar calcite; (2) microcrystalline calcite; and (3) botryoidal aragonite – each with ferruginous materials. Results showed that all domains of speleothems can take up >99% actinides, irrespective of valence state and pH (1–6 range) of the solution. However, distribution coefficients were found to be at a maximum in aragonite for most of the actinides. Such data are very important for long-term performance and safety assessments of the deep geological repositories planned for the disposal of high-level nuclear wastes.

A new protocol for the quantitative determination of zeolite-group mineral compositions by electron probe microanalysis (wavelength-dispersive spectrometry) under ambient conditions, is presented. The method overcomes the most serious challenges for this mineral group, including new confidence in the fundamentally important Si-Al ratio. Development tests were undertaken on a set of natural zeolite candidate reference samples, representing the compositional extremes of Na, K, Cs, Mg, Ca, Sr and Ba zeolites, to demonstrate and assess the extent of beam interaction effects on each oxide component for each mineral. These tests highlight the variability and impact of component mobility due to beam interaction, and show that it can be minimized with recommended operating conditions of 15 kV, 2 nA, a defocused, 20 μm spot size, and element prioritizing with the spectrometer configuration. The protocol represents a pragmatic solution that works, but provides scope for additional optimization where required. Vital to the determination of high-quality results is the attention to careful preparations and the employment of strict criteria for data reduction and quality control, including the monitoring and removal of non-zeolitic contaminants from the data (mainly Fe and clay phases). Essential quality criteria include the zeolite-specific parameters of R value (Si/(Si + Al + Fe3+), the 'E%' charge-balance calculation, and the weight percent of non-hydrous total oxides. When these criteria are applied in conjunction with the recommended analytical operating conditions, excellent inter-batch reproducibility is demonstrated. Application of the method to zeolites with complex solid-solution compositions is effective, enabling more precise geochemical discrimination for occurrence-composition studies. Phase validation for the reference set was conducted satisfactorily with the use of X-ray diffraction and laser-ablation inductively-coupled plasma mass spectroscopy.

Oscarkempffite, ideally Ag10Pb4(Sb17Bi9)∑=26S48, is a new mineral species found in old material (1929–30) from the Colorada vein, Animas mine, Chocaya Province, Department of Potosi, Bolivia. It is associated with aramayoite, stannite, miargyrite, pyrargyrite and tetrahedrite. Oscarkempffite forms anhedral grains and grain aggregates up to 10 mm across. The mineral is opaque, greyish black with a metallic lustre; it is brittle without any discernible cleavage. In reflected light oscarkempffite is greyish white, pleochroism is distinct, white to dark grey. Internal reflections are absent. In crossed polars, anisotropism is distinct with rotation tints in shades of grey. The reflectance data (%, air) are: 39.9, 42.6 at 470 nm, 38.6, 41.7 at 546 nm, 38.1, 41.2 at 589 nm and 37.3, 40.6 at 650 nm. Mohs hardness is 3–3½, microhardness VHN50 exhibits a range 189–208, with a mean value 200 kg mm–2. The average results of four electron-microprobe analyses in a grain are: Cu 0.24(7), Ag 14.50(8), Pb 11.16(14), Sb 28.72(16), Bi 24.56(17), S 20.87(5), total 100.05(6) wt.%, corresponding to Cu0.24Ag9.92Pb4.00Sb17.36Bi8.64S47.84 (on the basis of Me + S = 88 apfu). The simplified formula, Ag10Pb4Sb17Bi9S48, is in accordance with the results of a crystal-structure determination. The density, 5.8 g cm–3, was calculated using the ideal formula. Oscarkempffite has an orthorhombic cell with a = 13.199(2), b = 19.332(3), c = 8.249(1) Å, V = 2116.3(5) Å3, space group Pnca and Z = 1. The strongest eight lines in the (calculated) powder-diffraction pattern are [d in Å(I)hkl]: 3.66(35)(122), 3.37(70)(132), 3.34(100)(250), 2.982(55)(312), 2.881(86)(322), 2.733(29)(332), 2.073(27)(004) and 2.062(31)(182). Comparison with gustavite, andorite and roshchinite confirms its independence as a mineral species.

The crystal structure of argentobaumhauerite is reported for the first time from a sulfosalt aggregate from Lengenbach deposit, Binntal, Switzerland. The chemical formula of argentobaumhauerite, calculated in agreement with the results of structure determination is Cu0.06Ag1.20Tl0.18Pb21.46Sb0.56As32.28S72.26. The difference from the idealized baumahuerite formula, Pb12As16S36, and from the formula of Ag – , Tl- and Sb-free baumhauerite from Moosegg, Austria, Pb11.80As16.28S35.92, expresses the Ag + As and Tl + As substitution for 2Pb. Argentobaumhauerite is triclinic, a = 7.9053(10), b = 8.4680(10), c = 44.4102(53) Å, α = 84.614(2), β = 86.469(2), γ = 89.810(2)°. V(cell) = 2954.16 Å3, space group P1. Baumhauerite Pb11.80As16.28S35.92 from Moosegg is triclinic, a = 7.884(4), b = 8.345(4), c = 22.811(11) Å, α = 90.069(8), β = 97.255(8), γ = 90.082(8)°, V(cell) = 1488.8(13) Å3, space group P1. Both minerals represent the N1,2 = 3;4 = 3.5 member of the sartorite homologous series, with As-rich slabs separated by zigzag layers of trigonal coordination prisms of lead. In argentobaumhauerite the sequence of alternating N = 3 and N = 4 slabs of baumhauerite is further modified by alternation of two distinct types of N = 4 slabs, those with Pb present in the slab interior and those with the interior Pb substituted by Ag + As. The length and arrangement of crankshaft chains of short As–S bonds differs between different slabs, and especially between the N = 4 slabs of baumhauerite and argentobaumhauerite. The name 'argentobaumhauerite' replaces the preliminary name 'baumhauerite-2a' (IMA-CNMNC; accepted proposal 15-F).

The crystal structure of hejtmanite, Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, from Mbolve Hill, Mkushi River area, Central Province, Zambia (holotype material) has been refined on a twinned crystal to R 1 = 1.88% on the basis of 4539 [|F| > 4|F|] reflections. Hejtmanite is triclinic, C1̅, a = 10.716(2), b = 13.795(3), c = 11.778 (2) , = 90.07(3), = 112.24(3), = 90.03(3), V = 1612(2) 3. Chemical analysis (electron microprobe) gives: Ta2O5 0.09, Nb2O5 1.27, ZrO2 0.65, TiO2 14.35, SiO2 23.13, BaO 26.68, SrO 0.19, FeO 11.28, MnO 15.12, Cs2O 0.05, K2O 0.33, F 3.82, H2Ocalc. 1.63, O = F 1.61, total 97.10 wt.%, where the H2O content was calculated from the crystal-structure refinement, with (OH F) = 4 apfu. The empirical formula, calculated on the basis of 20 (O F) anions, is of the form (Si2O7)2(XO)4(XP)2, Z=4: (Ba1.82K0.07 Sr0.02)Σ1.91(Mn2.33 Zr0.04Mg0.03)Σ3.95(Ti1.88Nb0.10Zr0.02)Σ2(Si2.02O7)2O2[(OH)1.89 F0.11]Σ2F2. The crystal structure is a combination of a TS (Titanium Silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H heteropolyhedral, O octahedral). The topology of the TS block is as in Group-II TS-block minerals: Ti ( Nb) = 2 apfu per (Si2O7)2 [as defined by Sokolova (2006)]. In the O sheet, five [6]MO sites are occupied mainly by Mn, less Fe2 and minor Zr and Mg, with <MOφ> = 2.198 (φ = O,OH), ideally giving Mn4 apfu. In the H sheet, two [6]MH sites are occupied mainly by Ti, with <MHφ> = 1.962 (φ = O,F), ideally giving Ti2 apfu; four [4] Si sites are occupied by Si, with < SiO> = 1.625 . The MH octahedra and Si2O7 groups constitute the H sheet. The two [12]Ba-dominant AP(1,2) sites, with <APφ> = 2.984 (φ = O, F), ideally give Ba2 apfu. Two (1,2) and two (1,2) sites are occupied by O atoms and OH groups with minor F, respectively, ideally giving (XO)4 = ()2 ()2=O2(OH)2 pfu. Two (1,2) sites are occupied by F, giving F2 apfu. TS blocks link via a layer of Ba atoms which constitute the I block. Simplified and end-member formulae of hejtmanite are Ba2(Mn,Fe2)4Ti2 (Si2O7)2O2(OH,F)2 F2 and Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, Z = 4. Hejtmanite is a Mn-analogue of bafertisite, Ba2 4 Ti2(Si2O7)2O2(OH)2F2.

The new mineral melanarsite, K3Cu7Fe3+O4(AsO4)4, was found in the sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. It is associated with dmisokolovite, shchurovskyite, bradaczekite, hematite, tenorite, aphthitalite, johillerite, arsmirandite, As-bearing orthoclase, hatertite, pharmazincite, etc. Melanarsite occurs as tabular to prismatic crystals up to 0.4 mm, separate or combined in clusters up to 1 mm across or in interrupted crusts up to 0.02 cm × 1 cm × 1 cm covering basalt scoria. The mineral is opaque, black, with a vitreous lustre. Melanarsite is brittle. Mohs' hardness is ∼4 and the mean VHN = 203 kg mm–2. Cleavage was not observed and the fracture is uneven. D calc is 4.39 g cm–3. In reflected light, melanarsite is dark grey. Bireflectance is weak, anisotropism is very weak. Reflectance values [R1–R2, % (λ, nm)] are 10.5–9.4 (470), 10.0–8.9 (546), 9.7–8.7 (589), 9.5–8.6 (650). The Raman spectrum is reported. Chemical composition (wt.%, electron microprobe) is K2O 10.70, CaO 0.03, CuO 45.11, ZnO 0.24, Al2O3 0.32, Fe2O3 6.11, TiO2 0.12, P2O5 0.07, As2O5 36.86, total 99.56. The empirical formula, based on 20 O apfu, is (K2.81Ca0.01)∑2.82(Cu7.02Fe3+ 0.95Al0.08Zn0.04Ti0.02)∑8.11(As3.97P0.01)∑3.98O20. Melanarsite is monoclinic, C2/c, a = 11.4763(9), b = 16.620(2), c = 10.1322(8) Å, β = 105.078(9)°, V = 1866.0(3) Å3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are 9.22(100)(110), 7.59(35)(1₃11), 6.084(17) (111), 4.595(26)(1₃31, 220, 2₃21), 3.124(22)(3₃31, 1₃51), 2.763(20)(400, 1₃52), 2.570(23)(043) and 2.473(16) (260, 2₃61, 350). Melanarsite has a novel structure type. Its crystal structure, solved from single-crystal X-ray diffraction data (R = 0.091), is based upon a heteropolyhedral pseudo-framework built by distorted Cu(1–3)O6 and (Fe,Cu)O6 octahedra and As(1–3)O4 tetrahedra. Two crystallographically independent K+ cations are located in the tunnels and voids of the pseudo-framework centring eight- and seven-fold polyhedra. The name reflects the mineral being an arsenate and its black colour (from the Greek μέλαν, black).

The crystal structure of gianellaite, [(NHg2)2](SO4)(H2O)x, cubic, F4̄3m, a = 9.521(6) Å V = 863.1(1.6) Å3, Z = 4, was solved by direct methods and refined to an R1 index of 2.1% based on 167 unique observed reflections collected on a three-circle rotating-anode (MoKα X-radiation) diffractometer equipped with multilayer optics and an APEX-II detector. In the structure of gianellaite, nitrogen-centred (NHg4)5+ tetrahedra share all corners to form a framework of tetrahedra with an ordered arrangement of interstitial (SO4)2– tetrahedra that show strong orientational disorder. Infrared spectroscopy in the principal O–H stretching region shows peaks at ∼3300 and 1600 cm–1, indicating the presence of (H2O), the position(s) of which could not be discerned in difference-Fourier maps.

The epidote-group nomenclature report by Armbruster et al. (2006) provides a clear and concise definition of the epidote group, and a set of consistent rules and naming conventions for establishing new subgroups and mineral species within what is now the epidote supergroup (Mills et al., 2009). In order to comply with these rules, it was decided to rename the already approved minerals hancockite, niigataite and tweddillite to epidote-(Pb), clinozoisite-(Sr) and manganipiemontite-(Sr), respectively. These names were already well established within the mineral community, and the renaming caused some controversy. Recent International Mineralogical Association guidelines (Hatert et al. 2013) have given priority to the historical provenance of names over nomenclature consistency. Hatert et al. (2013) state as a main principle that "retroactivity will not be applied", but that "Every change in nomenclature has to go through the CNMNC, and is examined on its own merit", thus establishing a mechanism for re-instating historical names on a case by case basis. The CNMNC (Commission on New Minerals, Nomenclature and Classification Committee of the International Mineralogical Association) has therefore decided, as an exception to the main principle, to re-instate hancockite, niigataite and tweddillite. In part to maintain the historical names but, more importantly, re-establish the link between the mineral names and their structural and chemical definitions.

In order to define the cathodoluminescence (CL) properties of magmatic topaz and its relation with trace-element composition, we studied topaz phenocrysts from the Ary-Bulak ongonite massif, Russia using a wide array of analytical techniques. Scanning electron microscopy CL panchromatic images reveal strong variations, which define micrometre-scale euhedral growth textures. Several truncations of these growth textures occur in single grains implying multiple growth and resorption events. The CL-spectra of both CLbright and -dark domains have a major peak in the near-ultraviolet centred at 393 nm. Cathodoluminescence images taken after several minutes of electron bombardment show decreasing emission intensity. Electron microprobe analyses indicate high F concentrations (average OH/(OH + F) = 0.04 calculated by difference, 100 wt.% – total from electron probe microanalyses), consistent with what has been found previously in topaz-bearing granites, and the OH stretching vibration (∼3653 cm–1) was detected in Raman spectra. Laser ablation inductively-coupled plasma mass spectrometry traverses performed across the CL textures detected trace elements at ppm to thousands of ppm levels, including: Fe, Mn, Li, Be, B, P, Nb, Ta, W, Ti, Ga, light rare-earth elements, Th and U. Lithium, W, Nb and Ta appear to be correlated with CL intensity, suggesting a role for some of these elements in the activation of CL in topaz. In contrast, no clear correlation was found between CL intensity and F contents, despite the fact that the replacement of OH for F is known to affect the cell parameters of topaz.

Structural modifications with temperature of adamite, Zn2(AsO4)(OH), were determined by single-crystal X-ray diffraction up to dehydration and collapse of the crystal structure. In the temperature range 25–400°C, adamite shows positive and linear expansion. Axial thermal expansion coefficients, determined over this temperature range, are αa = 1.06(2) × 10–5 K–1, αb = 1.99(2) × 10–5 K–1, αc = 3.7(1) × 10–6 K–1 and αV = 3.43(3) × 10–5 K–1. Axial expansion is then strongly anisotropic with αa:αb:αc = 2.86: 5.38 : 1. Structure refinements of X-ray diffraction data collected at different temperatures allowed us to characterize the mechanisms by which the adamite structure accommodates variations in temperature. Expansion is limited mainly by edge sharing Zn(2) dimers along a and by edge sharing Zn(1) octahedra chains along c; on the other hand, connections of polyhedra along b, the direction of maximum expansion, is governed by corner sharing. Increasing temperature induces mainly an axial expansion of Zn(1) octahedron, which becomes more elongated, and no significant variations of the Zn(2) trigonal bipyramids and As tetrahedra. Starting from 400°C, deviation from a linear evolution of unit-cell parameters is observed, associated with some deterioration of the crystal, a sign of incipient dehydration. The process leads to the formation of Zn4(AsO4)2O.

Proposal 16-C was accepted by the Commission on New Minerals and Mineral Names of the International Mineralogical Association, and parabariomicrolite is discredited as identical to hydrokenomicrolite-3R. There are now two type localities: Alto do Giz pegmatite, Equador Co., Rio Grande do Norte, Brazil and Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil.