The location and some characteristics of nine veins containing nigerite are reported. These veins are part of the province of tin-tantalum veins of central Amapá. They are intrusive in andalusite schist and commonly consist of pegmatite in the centre and of quartz-mica rock at the margins. The nigerite can occur in the pegmatite as well as in the quartz-mica rock; its presence in a sample of quartz-sillimanite rock is also mentioned. In both pegmatite and quartz-mica rock, the common associated translucent heavy minerals are cassiterite, tourmaline, chrysoberyl, and occasionally andalusite, sillimanite, and garnet. Associated minerals in the quartz-sillimanite rock are cassiterite and chrysoberyl. Nigerite and cassiterite commonly occur together but are not found in the presence of gahnite. A possible explanation for this is given.

The nigerite of Amapá occurs as thin hexagonal plates, transparent and golden brown, amber-yellow or colourless, with diameters from microscopic up to a few millimetres. The sizes and the optical sign of this nigerite are the same as those of Nigeria and of Siberia, whereas Portuguese nigerite occurs in very fine grains and is mostly optically negative. The existence of alluvial nigerite is reported.

The original description of the hydroxide perovskite jeanbandyite gives a formula (Fe1–x3+,□x)(Sn1–y,□y) (OH)6 (□= vacancy), which implies the possibility of stoichiometric vacancies at B and B' sites. The validity of this formula has been questioned subsequently. Furthermore, jeanbandyite has metrically a cubic unit cell, but it is optically uniaxial. It is clear that a structure determination is needed to clarify the nature of this enigmatic mineral. Previous studies could find no crystals of sufficient quality for structure determination using X-ray diffractometers available at the time. Crystals of jeanbandyite from Hingston Down, Cornwall, UK and the type locality Llallagua, Bolivia, have been found that are of a quality that allows structure refinement by single-crystal X-ray diffraction. Structural data for crystals from each locality are presented that clarify the nature of jeanbandyite and raise some interesting questions concerning the significance of partially deprotonated states in perovskite-type structures. The structures of both jeanbandyite crystals are cubic with space group Pn3 and unit-cell parameters a = 7.658(2) Å (Llallagua) and 7.6427(2) Å (Hingston). The octahedral tilt system is a+a+a+ and corresponds to that of the aristotype of BB'(OH)6 hydroxide double perovskites. Structure determination demonstrates that B is very Fe3+-rich and B' is filled by Sn, thereby requiring revision of the general jeanbandyite formula to Fex3+Fe(1–x)2+Sn(OH)(6–x)Oxfor 1≥ × > 0.5, with an ideal end-member formula Fe3+Sn(OH)5O. As such, jeanbandyite corresponds to oxidized natanite with partially deprotonated oxygen sites. This stoichiometry cannot be represented in space group Pn3̄ for the observed unit cell as it implies more than one non-equivalent oxygen atom. Consequently, it is inferred that there is no long-range ordering of deprotonated oxygen sites. It is, however, conceivable that the uniaxial optical character of jeanbandyite is linked to the local short-range order of deprotonated domains.

X-ray and thermal studies in the system MnO-O-H2O show that the transformations groutite(α-MnOOH)-ramsdellite(MnO2)-pyrolusite(MnO2) are topotactic, with the a, b, and c directions of all three corresponding. The reactions proceed by migration of manganese atoms and, where appropriate, protons. Pure single crystals of ramsdellite could not be prepared by heating groutite, even though the two structures are very similar.

Kaalijärv is a crater-lake on the estate Kaali (järv = lake in the Estonian language) at 58°24′N., 22°40′E. Known in German as Sall, this locality is 20km. NE. of Arensburg (= Kuresaare) on the Baltic island of Oesel (= Saaremaa). On the level agricultural country a thickly wooded knoll 6–7 metres high is seen. Inside there is a crater 15½ m. in depth, the circular rim of which measures 92–110 m. across. The lake at the bottom is about 60 m. across. The rock of the district is horizontally bedded Silurian dolomite with a covering of glacial deposits. The rim of the crater consists of fragmentary materials, and the steeper inner slopes show the beds of dolomite dipping outwards as a dome at angles of 30–40°. Near by, on an area of ¾ sq. km., are five other smaller craters similar in character, and at least three other depressions that have been filled with stones collected from the tilled fields.

Fluid flow through a fractured granite core and leaching experiments on granite powder (at constant temperatures of 50 and 100°C and during cooling from 100 to 50°C) indicate that the dissolved silica content of the fluids originates from the dissolution of feldspars and phyllosilicates. The dissolution of quartz is not ruled out but it should be a minor phenomenon. The precipitation of quartz may control the dissolved Si content during constant temperature leaching. During cooling from 100 to 50°C chalcedony, alumino-silicates, and chlorite are all capable of precipitation, possibly leading to some clogging or sealing of fissures.

When one optic axis of a biaxial crystal has been located accurately by the usual orthoseopic or conoscopic methods, the second may be located by determining the extinction positions at normal incidence and applying the Biot-Fresnel construction. When use is made of the extinction directions associated with two or more wave normals inclined to the section, this method gives more reliable values of the optic axial angle than can be obtained by the doubling of the angle V over the pole of a bisectrix. If the optic axes have been located with sufficient accuracy by this procedure, then this also determines the orientation of the indicatrix.

Argentotetrahedrite-(Cd), Ag6(Cu4Cd2)Sb4S13, has been approved as a new mineral species by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association using samples from Rudno nad Hronom, Slovak Republic. It occurs as anhedral grains up to 30 μm in size, steel-grey to black in colour, with a metallic lustre, in association with greenockite and other tetrahedrite-group minerals [argentotetrahedrite-(Zn) and tetrahedrite-(Zn)], earlier base-metal minerals, Ag sulfides and sulfosalts (acanthite, pyrargyrite and polybasite) and later galena. Argentotetrahedrite-(Cd) is isotropic, grey in colour, with a creamy tint and rapidly (tens of minutes) tarnishes to orange–brown. Reflectance data for Commission on Ore Mineralogy (COM) wavelengths in air are [λ (nm), R (%)]: 470, 30.4; 546, 30.3; 589, 30.3; and 650, 28.7. The chemical formula of the samples studied, recalculated on the basis of ΣMe = 16 atoms per formula unit, is: (Ag3.28Cu2.72)Ʃ6.00[Cu4(Cd1.68Fe0.27Zn0.16)]Ʃ6.11(Sb3.71As0.15)Ʃ3.86S12.79. Argentotetrahedrite-(Cd) is cubic, I$\bar{4}$3m, with a = 10.65(2) Å, V = 1208(4) Å3 and Z = 2. Argentotetrahedrite-(Cd) is isotypic with other members of the tetrahedrite group. The structural relationship between argentotetrahedrite-(Cd) and other members of the freibergite series are discussed and previous findings of this species are briefly reviewed.

Although the mineral gyrolite has long been known to occur in the British Isles, namely in the basalt lavas of Skye, Mull, and the Treshnish Islands, &c., off the west coast of Scotland, and has more recently been described from the cliffs between Ardtornish Bay and the fault of Dearg Allt in Argyllshire on the mainland, no instance of its occurrence in the lavas of the north of Ireland has hitherto been recorded.

The examination, however, of a large number of specimens collected both for me and by myself during the past year and a half has shown that the mineral, though occurring in small quantity relative to the other zeolites with which it is associated, is fairly widely distributed throughout the harder lavas in the neighbourhood of Belfast.

Published data from pyrrhotine-vapour equilibrium experiments are used to make inferences concerning the high-temperature thermodynamic mixing properties of pyrrhotine. Darken's quadratic formalism provides the justification for plotting activity of sulphur data against (1−X)2, where X is used in Fe1−XS to express the composition of non-stoichiometric pyrrhotine. Such plots show that the thermodynamic behaviour of pyrrhotine appears to be different on either side of X = 0.125, the Fe7S8 composition.

Determinations of Cu in separate phases of three olivine-hypersthene and one olivine-bronzite chondrites show that it is very strongly concentrated in the taenite; appreciable amounts are present in the olivine, less in the pyroxene plus plagioclase; it is probable that the copper found in the ‘unattracted, attacked’ fraction is present as metallic copper, and that very little is present in the sulphides.

Tricalcium disilicate, first described by Shepherd, Rankin, and Wright in their investigations on the lime–silica and lime–alumina–silica systems has since been reported as a constituent of technical slags. An account has also been given of its occurrence as a reaction product in a glass furnace.

In the ternary system CaO–Al2O3–SiO2 the compound forms with pseudowollastonite–gehlenite and larnite–gehlenite two three-phase equilibrium assemblages, associations which are in part recorded in the technical products.

G. V. Wilson recorded the disilicate together with wollastonite and melilite in reconstituted limestone fragments enclosed in glass, while S. G. Gordon has described and presented an analysis of a slag composed of pseudowollastonite and the 3:2-compound approaching in composition that of the binary eutectic in the synthetic system.

In the course of a study of certain cerium minerals, a spectrogram of churchite was taken and it was noticed that the cerium lines were barely visible, whereas the yttrium lines were very strong. We therefore decided to re-investigate this species.

Churchite was originally described by A. H. Church in 1865, and named by C. G. Williams in the same year. The specimens were collected by R. Talling from an unnamed locality in Cornwall. It has only been analysed once, by Church, who showed it to be a hydrated phosphate of rare-earths and lime; his quantitative data have been recalculated and included in table I. Church obtained qualitative reactions for the cerium group of rare-earths, and for cerium itself, but made no attempt to determine the ratio of cerium to yttrium earths; he assumed a mean molecular weight for the rare-earths which would correspond to R2O3 324, essentially a mixture of cerium earths with but little yttria, but did not adduce any evidence for this assumption.

Iron ore sinters prepared for the blast furnaces at Scunthorpe, Humberside, comprise iron oxides bound in a matrix of aluminium- and silicon-rich calcium ferrites with some calcium orthosilicate and a residual silicate glass. A super-silicon-deficient clinopyroxene with up to half of the Si in the chain replaced by Fe3+ and Al3+ precipitates from the glass in some areas. The iron oxides are principally magnetite and hematite with some wüstite in highly reduced areas. The calcium orthosilicate has been previously reported as the mineral larnite, β-Ca2SiO4. This study found a range of Fe for Ca substitution and three polymorphs were recognised: the range Ca2SiO4 to Ca1.85Fe0.15SiO4 has the structure of larnite; the range Ca1.85Fe0.15SiO4 to Ca1.6Fe0.4SiO4 has the structure of bredigite, α′-Ca2SiO4. Iron substitution beyond this, and up to a maximum of about Ca1.5Fe0.5SiO4, was not recognisable as a polymorph of Ca2SiO4, but an orthorhombic cell is tentatively proposed. The complex ferrite SFCA (silico-ferrite of Ca and Al) is variable in composition, but has a minimum of about 3 wt. % Al2O3 and contains 20 wt. % CaO and SiO2 with a Ca: Si ion ratio of about 2 : 1. A C-face centred monoclinic cell has been deduced: a 15.70, b 9.70, c 8.48 Å; β 105°30′. The Al appears critical for the formation of SFCA in sinter; without it, a eutectic of magnetite and bredigite precipitates in preference.

Tangdanite, ideally Ca2Cu9(AsO4)4(SO4)0.5(OH)9·9H2O and monoclinic, is a new mineral species (IMA No. 2011-096) occurring in the Tangdan and Nanniping mines, southeast Dongchuan copper mining district, Dongchuan County, Kunming City Prefecture, Yunnan Province, P. R. China (26°11’N 103°51’E). The mineral is found in the oxidized zone (gossan) of an As-bearing Cu sulfide deposit and is clearly of supergene origin. Associated minerals are chalcopyrite, bornite, chalcocite, covellite, tennantite, enargite, cuprite, malachite, azurite, copper and brochantite. Crystals form radiating or foliated aggregates of flaky crystals up to 3 mm, flattened parallel to (100) and elongated along [001]. It is emerald green with a light green streak, translucent and has a pearly to silky lustre. It is sectile having perfect cleavage on {100} although neither parting nor fracture was observed. No fluorescence in long- or short-wave ultraviolet radiation was observed. The hardness is VHN50 42.0−43.6, mean 42.8 kg mm−2 (2−2½ on the Mohs scale). The density measured by pycnometry is 3.22 g cm−3 (Ma et al., 1980). The calculated density from the empirical chemical formula is 3.32 g cm−3. The compatability index gives 1 − (Kp/Kc) = −0.041 (good). The empirical formula (based on 36 O a.p.f.u) of tangdanite is Ca2.05Cu9.08(As1.03O4)4(S0.63O4)0.5(OH)9·9H2.04O. The simplified formula is Ca2Cu9(AsO4)4(SO4)0.5(OH)9·9H2O. The strongest five reflections in the X-ray powder-diffraction pattern [d in Å(I) (hkl)] are: 4.782(100) ( 1 1), 4.333(71) (6 0 2), 5.263(54) ( 0 2), 3.949(47) (8 0 2) and 2.976(46) ( 1 1). The unit-cell parameters are a = 54.490(9), b = 5.5685(9), c = 10.4690(17) Å, β = 96.294(3)o, V = 3157.4(9) Å3, Z = 4. Its structure was solved and refined in space group C2/c, with R = 0.110.

Bariopharmacoalumite-Q2a2b2c, Ba0.5(Cu,ZnO)0.1H0.6[Al4(OH)4(As0.9Al0.1O4)3]·5.5H2O, from the south mine of the old copper mine at Cap Garonne, France, has a 2 × 2 × 2 I-centred tetragonal superstructure of the basic pharmacosiderite-type structure. Cell parameters are a = 15.405(2) Å and c = 15.553(3) Å. The structure was determined and refined in I 2m to R 1= 0.057 for 2697 reflections with I > 2σ(I), using synchrotron X-ray data on a twinned crystal. The origin of the superlattice cell doubling was determined to be due predominantly to the ordering of Ba atoms in half of the [0 0 1] channels, centred at (0, 0, 0) and (½, ½, 0). The other channels, centred at (½, 0, 0) and (0, ½, 0), were found to be occupied by corner-connected chains of Cu/Zn-centred square planar units.

Microlite-group minerals occur as common replacement products after primary and secondary columbite-group minerals (CGM) in albitised blocky K-feldspar and in coarse-grained, muscovite-rich units of the Schinderhübel I, Scheibengraben and Bienergraben beryl–columbite pegmatites in the Maršíkov District (Silesian Unit, Bohemian Massif, Czech Republic). Textural and compositional variations of microlite-group minerals were examined using electron probe micro-analyses and microRaman spectroscopy (μRS). A complex post-magmatic evolution of the pegmatites and the following microlite populations (Mic) and related processes were found: (1) precipitation of U, Na-rich and F-poor Mic I on cracks in CGM; (2) alteration of Mic I to U-rich together with Na- and F-poor Mic II; and (3) partial replacement of Mic I and II by Mic III with a distinct Na, U and Ti loss and Ca and F gain. Stage (2) includes an extensive leaching of Na, without U loss. The final stage (3) produced euhedral-to-subhedral oscillatory zoned Ca and F enriched Mic III with distinctly different composition to the previous F-poor and A-site vacant Mic II. Aggregates of fersmite are associated commonly with Mic III. Distal Mic IIId occurs locally on cracks in K-feldspar or quartz, with compositions analogous to Mic III. Compositional variations and textural features of microlite-group minerals during dissolution–reprecipitation processes serve as sensitive tracers of post-magmatic evolution in granitic pegmatites recording complex interactions between magmatic pegmatite units and externally derived, hydrothermal metamorphic fluids.

Sporadic small garnet granulite and two-pyroxene granulite xenoliths found in the carbonatite tuffs and lavas near Fort Portal, South West Uganda, are chiefly silica-saturated and rich in Al2O3 (> 20 wt. %) and Na2O (c. 2 to 4 wt. %). Three REE patterns are distinguished: LREE enriched—HREE depleted with a positive Eu anomaly; LREE depleted—HREE relatively enriched and flat; and LREE slightly enriched with a very weak Eu anomaly and high overall REE. The xenoliths are considered to represent original basaltic melts and fractional crystallisation products, varying with the dominance of the clinopyroxene, plagioclase or olivine crystallising phase. It is thought that REE abundances were established before metamorphism.

The clinopyroxenes are low-jadeitic augites, the orthopyroxenes, aluminous hypersthenes and the garnets, pyrope-almandine with constant grossularite. Plagioclase varies with increasing metamorphic grade from labradorite to andesine-oligoclase. Scapolite (meionite), alkali-feldspar, quartz, mica, amphibole, rutile and apatite are minor phases and some appear to be metasomatic.

Calculated temperatures of metamorphic equilibration range from 580 to 800°C at pressures > 4 kbar for the two-pyroxene granulites and > 6 kbar for the garnet granulites. A known geophysical discontinuity marking a density change at 16 km in the Western Rift may be due to the presence of two-pyroxene granulite, calculated to become garnet-bearing at depths greater than 23 km. The absence of proven omphacite-bearing eclogite xenoliths (with no plagioclase) indicates that the greatest depth of crustal sampling by the carbonatite in the Fort Portal field is about 25 km which could be the depth of the Moho in this area.

The quartz-monzonitic intrusion of ‘Botro ai Marmi’ in Tuscany, Italy, can be considered to be a typical example of an intrusion-centred magmatic hydrothermal system. The evolution of hydrothermal fluids in the ‘Botro ai Marmi’ intrusion was investigated using fluid-inclusion analyses to provide suitable physico-chemical constraints on the fluids involved in the late- to post-magmatic hydrothermal activity that affected the intrusion, providing inferences on their origin and variations of temperature and pressure with time.

This work demonstrates that the earliest fluids circulating in the ‘Botro ai Marmi’ intrusion were high-temperature brines exsolved directly from the crystallizing magma. This fluid circulated in the intrusion under lithostatic conditions (P > 90 MPa, T > 540°C). A second evolutionary stage of the magmatic hydrothermal system is marked by the transition from lithostatic (>90 MPa) to hydrostatic dominated conditions (50 to 10 MPa). In this stage the fluids are also interpreted to be mainly orthomagmatic in origin but unmixed in a high-salinity brine and in a low-salinity vapour aqueous phase, at a temperature ranging from ~500 to 300°C. These fluids were responsible for the potassic alteration facies. At a later stage of hydrothermal evolution, abundant meteoric dominated fluids entered the system and are associated with propylitic alteration. This event marks the transition from a magmatic-hydrothermal system to a typical hydrothermal (‘geothermal’) system, which can be assumed to be similar to some extent to the nearby active high-enthalpy geothermal system of Larderello. Low-temperature and low-salinity meteoric water-dominated fluids characterize the latest stage of the ‘Botro ai Marmi’ hydrothermal system.