Sazhinite-(La) is a new mineral from the Aris phonolite, Windhoek, Namibia. It occurs in vesicles within the phonolite, together with other species crystallized from late-stage hydrothermal fluids: natrolite, aegirine, microcline, apophyllite, sphalerite, analcime, fluorite, villiaumite, hydroxylapatite, galena, makatite, quartz, eudialyte, kanemite, tuperssuatsiaite and korobitsynite. Sazhinite-(La) forms small euhedral crystals up to 1 mm long and 0.4 mm wide, elongated along [001] and flattened on (010), exhibiting the forms {h0l}, {100} and {001}. It has good cleavage parallel to {010} and {001}. Twinning was not observed. Crystals are brittle with a Mohs hardness of 3, creamy white with a white streak, vitreous to pearly lustre, and translucent to transparent. In plane-polarized light, crystals are colourless with a = Z, b = Y, c = X. It is biaxial positive with α = 1.524, β = 1.528, γ = 1.544, all ±0.002, 2Vz(obs) = 46(1)°, and 2Vz(calc.) = 53.6°.

Sazhmite-(La) is orthorhombic Pmm2, a = 7.415(2), b = 15.515(3), c = 7.164(1) Å, and V = 824.2 Å3. One crystal was studied by X-ray diffraction, electron microprobe and secondary ion mass spectrometry (SIMS) microanalysis, leading to the average composition (Na2.87K0.02Sr0.01)Σ2.90 [La0.41Ce0.35Pr0.02Nd0.04(Sm,Gd,Dy,Er,Yb)Σ0.01Th0.09U0.01Y0.01Zr0.01Ca0.08Li0.01]Σ1.04 (S15.87S0.06B0.01) (O14.86F0.14).(H2O)2.

Weighted full-matrix least-squares refinement on 3369 reflections yielded Rall = 3.8%. The structure is built of corrugated [Si6O15]6- layers linked by [7]-coordinated REE and R4+ cations. This framework leaves channels that contain three [5]- and [6]-coordinated Na cations per formula unit that compensate for the residual charge on the silicate layers. The SIMS analyses confirm a Na content of 3 atoms per formula unit, leading to an ideal formula of Na3LaSi6O15(H2O)2. The third Na atom is bonded to H2O groups and therefore the total content of both Na and H2O may be reduced to 2 and 1 per formula, respectively. The depletion in Na allows for the entrance of high-charge cations such as Th4+.

Platinum group mineral (PGM) assemblages in the Platreef at Sandsloot, northern Bushveld Complex, in a variety of lithologies reveal a complex multi-stage mineralization history. During crystallization of the Platreef pyroxenites, platinum group elements (PGE) and base-metal sulphides (BMS) were distributed thoughout the interstitial liquid forming a telluride-dominant assemblage devoid of PGE sulphides. Redistribution of PGE into the metamorphic footwall by hydrothermal fluids has formed arsenide-, alloy- and antimonide-dominant assemblages, indicating a significant volatile influence during crystallization. Serpentinization of the footwall has produced an antimonide-dominant PGM assemblage. Parts of the igneous reef were subjected to alteration by a late-stage, Fe-rich fluid, producing ultramafic zones where the telluride-dominant assemblage has been recrystallized to an alloy-dominant one, particularly rich in Pt-Fe and Pd-Pb alloys. A thin, small-volume zone of PGE-BMS mineralization along the base of the hangingwall contains a primary PGM assemblage that is locally altered to one dominated by Pt/Pd germanides. This is thought to have formed when the new pulse of Main Zone magma entered the chamber, and scavenged PGE from the underlying Platreef pyroxenites. That each major rock type at Sandsloot contains a distinctive PGM assemblage reflects the importance of syn- and post-emplacement fluid and magmatic processes on the development of Platreef mineralization.

Structural modifications as a function of the degree of order (Q) in FeTa2O6 ferrotapiolite have been characterized by means of single-crystal X-ray diffraction (SC-XRD). A total of 26 datasets covering the range of Q between 0.154 and 1 have been obtained by thermal treatments followed by quenching of natural tapiolite crystals. Ordering of Fe2+ at the A sites and of Ta5+ at the B sites causes a linear increase in the a/c lattice constants ratio, as a consequence of a linear decrease of the c dimension and only slight modifications of the a parameter. Calibration of a/c vs. Q represents a very useful tool for a rapid determination of the degree of order of tapiolite samples. Polyhedral volumes of the two octahedral sites vary linearly with Q as a consequence of the different ionic radii of the two species. Both the sites remain almost regular at all Q values but the B site shows an increasing off-centre displacement of the cation with increasing Q. Observed structure factors of supercell reflections, characterized by l ≠ 3n, increase linearly as a function of Q, thus representing a further tool for a quick evaluation of the degree of order.

High-resolution imaging of electron-transparent samples using a scanning electron microscope, here termed low voltage (LV) STEM, is a new and valuable technique for studying Earth and planetary materials. The most effective method of LV-STEM imaging uses a pair of electron detectors positioned side-by-side beneath the thin sample. The detector directly underlying the sample forms bright-field images dominated by mass-thickness contrast. Activation of the detector offset from the sample yields dark-field images with a greater component of atomic number contrast. LV-STEM images with significant diffraction contrast can also be obtained, but require careful positioning of the sample relative to the electron detectors. In this study LV-STEM was used successfully to image sub-μm sized kaolinite crystals and tens of nm-sized etch pits on the gold-coated surfaces of weathered feldspar grains. Dark-field LV-STEM was also especially effective for characterizing very fine-scale intergrowths of Mg- and Fe-rich phyllosilicates within uniformly thin samples of the Murchison meteorite prepared using the focused ion beam (FIB) technique. LV-STEM is a quick and easy method for characterizing the morphology and internal structure of mineral and rock samples and may prove to be especially useful in geomicrobiology research.

‘Green rusts’ are a group of reduced Fe hydroxides with a pyroaurite-like structure. In a new occurrence, green rust is present as a 45–60 mm thick band which lies just below the surface (∼4 mm) of an ochreous deposit at an abandoned coal mine site. The sample is characterized by the presence of μm-sized hexagonal crystals which have been identified from SEM imaging. Chemical analyses reveal an Fe(II):Fe(III) ratio which is close to the characteristic 2:1 ratio, and XRD analysis identifies the material by characteristic lattice spacings. The green rust layer also contains aragonite which is not present in the surrounding ochre. Green rusts are important as they have the potential to be used in water treatment.

Natrocarbonatite lavas erupted from hornitos T37B and T49B at Oldoinyo Lengai (Tanzania) during 23–30 July, 2000 are unusual in containing sylvite and fluorite microcrysts together with fluorite-nyerereite intergrowths. The latter are relatively coarse grained and exhibit granular textures indicative of slow crystallization rates relative to those of their host subaerial lavas. Fluorite microcrysts are considered to be derived by the fragmentation of the fluorite-nyerereite clasts. Sylvite microcrysts contain inclusions of ferroan alabandite [(Mn0.67-0.71Fe0.33-0.29)S] and are poor in Na (1.9–7.7 wt.% Na; 6.1–23.4 mol.% NaCl). Intergrowth and microcrystal fluorite contains 1–3.5 wt.% Sr. Intergrowth nyerereite has a composition similar to that occurring as bona fide phenocrysts. The groundmass of lava erupted from hornito T37B contains nyerereite microphenocrysts (4–8 wt.% BaO) that are epitaxially mantled by barian nyerereite (12–20 wt.% BaO). The latter are compositionally and texturally distinct from the groundmass phase X, which is considered to be a burbankite-group mineral. The fluorite-nyerereite clasts are considered to be derived from the magma chamber underlying hornitos T37B and T49B, and thus representative of some of the products of crystallization of natrocarbonatite magma under hypabyssal conditions. The origins of the sylvite microcrysts cannot, as yet, be determined.

Allanite is present in most samples of the tonalitic Bell Island Pluton, with an average mode near 0.05 wt.%. Allanite occurs as cores in igneous epidote-clinozoisite and exhibits characteristic and consistent zoning patterns. REE-rich cores (All40-70) grade out towards epidote-clinozoisite with REE below electron microprobe detection limits. La, Ce and Pr contents are highest in the REE-rich cores of zoned crystals. Nd and Sm contents both initially increase as total REE decreases and are highest in intermediate zones. Y contents are generally low throughout, but tend to be highest in analyses with A115-20. The zoning behaviour exhibited by the allanite, specifically the rimward increases in Nd, Sm, and Y, cannot be accounted for by simple fractionation and are best explained by increases in allanite/ melt partition coefficients (Kd values) for these elements during crystallization. We propose that the variation in Kd values reflects modification of the allanite structure with changing REE content. These modifications are manifested by changes in colour, extinction, and pleochroism within the zoned crystals and include changes in unit-cell volume and dimensions. The changes in Kd values are large enough to result in crossing REE patterns within single allanite crystals. Fractional crystallization of zoned allanite can have noticeable effects on LREE contents and La/Sm (and almost certainly La/Lu) in magmas. In the Bell Island pluton, 80% of La, but <3% of Y is contained in allanite. Although some of the variation in the LREE chemistry of the pluton is attributable to statistical sampling error, much of it appears to reflect petrogenetic processes that controlled LREE abundance and, ultimately, allanite mode. One sample of Bell Island tonalite is depleted in LREE and has low La/Lu and La/Sm. These chemical features can be modelled by fractionation of zoned allanite.

Recognition of widespread carbonate volcanism in central Spain has led to another case in France, of similar age (23–0 Ma) but with entirely new features. More than 100 new carbonate volcanoes are indicated already, adding a wholly unexpected dimension to this form of activity. Eruptions form layers, mostly of glassy nephelinite fragments in a dolomitic matrix, but some layers are largely dolomite. Major new findings are phenocrysts of dolomite, magnesite and calcite in silicate glass, and spectacular dolomite-nephelinite melt immiscibility, neither recorded previously. Most volcanic carbonatites are Ca rich, and dolomite is rare. The Limagne dolomites share links with those in Spain and Zambia, with chromite a hallmark in all three. Limagne is exceptional in being the first case where dolomite has erupted with co-genetic silicate melt. Mantle debris and magnesite indicate a source within ∼ 100–150 km. Chromite in the dolomite globules, and in the enclosing silicate glass, is similar to that in high-temperature kimberlites, indicating immiscibility in the deep mantle. Recognition of two large, previously undetected provinces of carbonate volcanism in Europe, where there has been active research for >200 y, must lead to the inference that similar cases may await discovery on other continents.

Hematite is a mineral the chemical composition of which rarely differs significantly from stoichiometric Fe2O3. As such, little attention has been paid to the mineral chemistry of hematite in Precambrian iron formations, where hematite forms monomineralic high-grade orebodies. Electron microprobe analysis of hematite from two iron-ore deposits, Cauê (Itabira district) and Gongo Soco, in the Palaeoproterozoic Itabira Iron Formation, Quadrilátero Ferrífero of Minas Gerais, Brazil, has revealed distinct variations in chemical composition with respect to Ti and Cr. Hematite containing Ti and/or Cr is of very local occurrence in the itabirite unit and shows a spatial relationship to hematitic, palladiferous gold-bearing veins (known as ‘jacutinga’), occurring either within the veins (adjacent to, or included in, palladiferous gold grains) or in their vicinity. Where present, titaniferous hematite (to ∼1.3 wt.% TiO2) is lepidoblastic and defines a pervasive tectonic foliation (S1). In contrast, Ti-free, chromiferous hematite (to ∼6.4 wt.% Cr2O3) characteristically occurs as inclusions in palladiferous gold within S1-truncating ‘jacutinga’. Replacement of granoblastic, Ti-free, chromiferous martite with relicts of magnetite by lepidoblastic, Cr-depleted, titaniferous hematite proves that Cr and Ti were mobile during metamorphism. Chromium was ultimately fractionated into the hematite found in auriferous aggregates within cross-cutting ‘jacutinga’. A positive correlation between Cr and Pt in bulk-rock samples from the Itabira district suggests that Cr is a potential prospective guide for Au-Pd-Pt-bearing hematitic veins (‘jacutinga’).

Stalactites formed by the chemical weathering of natrocarbonatite lava decorate the roofs of hollow inactive hornitos at Oldoinyo Lengai, Tanzania. The stalactites are composed principally of trona with lesser and very variable amounts of nahcolite, (NaHCO3), thermonatrite (Na2CO3.H2O), aphthitalite [(K,Na)3Na(SO4)2], kogarkoite [Na3(SO4)F], schairerite [Na21 (SO4)7F6Cl], halite and sylvite. Stalactites are considered to form by the evaporation of Ca-free highly alkaline brines seeping from the altered lavas which form the roofs of the hornitos. The principal subaerial weathering products of natrocarbonatite, i.e. pirsonnite, gaylussite, shortite and calcite are not found in the stalactites and are retained in the altered lavas of the homito roof. Fluorine required for the formation of kogarkoite and schairerite is derived from the decomposition of fluorite at high pH (>10). Sulphur is derived from the decomposition of gregoryite.

A synthetic analogue, Ca(Ti0.6Al0.2Ta0.16Nb0.04)OSiO4, of an aluminoan tantalian titanite previously described from Craveggia pegmatite (Piemonte, Italy) has been prepared by a ceramic synthesis technique and its crystal structure determined by Rietveld analysis of the powder X-ray diffraction pattern. The synthetic Al-Ta-Nb-rich titanite adopts space group A2/a implying that substitutions at the single octahedral site destroy the coherence of the off-centering of octahedral chains in the titanite structure resulting in a P 21/a → A2/a phase transition. Unit-cell dimensions obtained for the Al-Ta-Nb-rich titanite are: a = 7.0649(1) Å; b = 8.7187(1) Å; c = 6.5701(1) Å; β = 113.755(1)°, V = 370.41(1) Å3. The extensive replacement of Ti by Al, Ta and Nb results in a considerable decrease in the distortion of all coordination polyhedra in the structure of this titanite. These structural data suggest that a solid solution CaTi1-x(Alx /2 [Ta,Nb]x /2)OSiO4 (0 ≤ x ≤ 0.4) adopting the titanite structure might exist.

Kapellasite, Cu3Zn(OH)6Cl2, is a new secondary mineral from the Sounion No. 19 mine, Kamariza, Lavrion, Greece. It is a polymorph of herbertsmithite. Kapellasite forms crusts and small aggregates up to 0.5 mm, composed of bladed or needle-like indistinct crystals up to 0.2 mm long. The colour is green-blue, the streak is light green-blue. There is a good cleavage parallel to ﹛0001﹜. Kapellasite is uniaxial negative, ω = 1.80(1), ε = 1.76(1); pleochroism is distinct, with E = pale green, O = green-blue. Dmeas = 3.55(10) g/cm3; Dcalc. = 3.62 g/cm3. Electron microprobe analyses of the type material gave CuO 58.86, ZnO 13.92, NiO 0.03, CoO 0.03, Fe2O3 0.04, Cl 16.70, H2O (calc.) 12.22, total 101.80, less O = Cl 3.77, total 98.03 wt.%. The empirical formula is (Cu3.24Zn0.75)Σ3.99(OH)5.94Cl2.06, based on 8 anions. The five strongest XRD lines are [d in Å (I/I0, hkl)] 5.730 (100, 001), 2.865 (11, 002), 2.730 (4, 200), 2.464 (9, 021/201), 1.976 (5, 022/202). Kapellasite is trigonal, space group Pml, unit-cell parameters (from single-crystal data) a = 6.300(1), c = 5.733(1) Å, V= 197.06(6) Å3, Z = 1. The crystal structure of kapellasite is based on brucite-like sheets parallel to (0001), built from edge-sharing distorted M(OH,Cl)6 (M = Cu, Zn) octahedra. The sheets stack directly on each other (…AAA… stacking). Bonding between adjacent sheets is only due to weak hydrogen and O…C1 bonds. The name is in honour of Christo Kapellas (1938–2004), collector and mineral dealer from Kamariza, Lavrion, Greece.

Kalungaite, PdAsSe, is a new mineral discovered in the Buraco do Ouro gold mine, Cavalcante town, Goiás State, Brazil. It occurs in a quartz-muscovite mylonite, related to a peraluminous granite, in platy anhedral aggregates along foliation planes. Associated ore minerals are gold, chalcopyrite, bohdanowiczite, an unnamed Pb-Bi-Se-S mineral, clausthalite, guanajuatite, stibiopalladinite, sperrylite and padmaite. Gangue minerals are muscovite, quartz and rare tourmaline and magnetite. Kalungaite is lead-grey, has a metallic lustre, a black streak and is brittle with uneven fracture. No cleavage was observed. The mineral has a micro-indentation hardness of VHN25 = 438 (range of 429–455 kg/mm2 from five indentations). Under reflected light, kalungaite is cream, or creamy grey adjacent to gold grains, has no internal reflections and is isotropic. Reflectance values in air (and in oil) are: 47.5 (33.3) at 470 nm, 46.9 (32.6) at 546 nm, 46.8 (32.6) at 589 nm and 48.0 (34.0) at 650 nm. The average of eight electron-microprobe analyses gives: Pd 41.32, As 27.49, Bi 0.35, Sb 1.59, Se 27.67 and S 1.22, total 99.64 wt. %, corresponding to Pd1.006(As0.950Sb0.034Bi0.004)Σ0.988(Se0.908S0.099)Σ1.007Kalungaite is cubic, space group Pa, a = 6.089(4) Å, V = 225.78 Å3, Z = 4. Dcalc is 7.59 g/cm3. The strongest seven X-ray powder-diffraction lines [d in Å(I)(hkl )] are: 3.027(75)(002), 1.838(100)(113), 1.172(95)(115, 333), 1.077(80)(044, 144, 334), 0.988(70)(116, 235, 253), 0.929(90)(335) and 0.918(70)(226). Kalungaite is interpreted as having formed from hydrothermal fluids of granitic origin, during syn-emplacement shearing and alteration, producing an unusual gold-platinum-group element deposit.

Extreme silver enrichment at the surface of the complex sulphide, tennantite (ideal formula: Cu12As4S13), occurs following exposure to alkaline solutions, and involves the development of an Ag-rich sulphide surface species. The tennantite has a low bulk Ag content of 0.3 at.%, and a percentage surface enrichment of Ag is thirty-six times that of the bulk. The techniques of X-ray photoelectron spectroscopy (XPS) and reflection extended X-ray absorption fine structure spectroscopy show the new phase to be a Ag sulphide species compositionally similar to cupriferous proustite ((Cu,Ag)3AsS3). Solution experiments and XPS depth profiling show that the surface is most depleted in Cu and Zn, and enriched in Ag compared to the bulk tennantite. Selective dissolution and reprecipitation at the tennantite surface cannot explain the enrichment of Ag relative to the bulk. Migration must have occurred and could have been driven by the leaching out of Cu which produces a metal-depleted surface, coupled to the relative incompatibility of Ag in the tennantite lattice. To account for the extreme enrichment at the surface, Ag must have diffused from depths of up to 9 nm, probably via structural weaknesses and vacancies in the tennantite lattice.