Showing papers in "Mineralogical Magazine in 2010"

Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones

Abstract: ABSTR ACT Studies of the inclusions contained in natural diamonds have shown the occurrence of minerals which must have formed at depths below the lithosphere and which may be closely matched with the silicate mineral assemblages determined by high pressure and temperature experimental studies for depths of 300 to 800 km in the Earth’s mantle. The inclusions come principally from two main depth zones: (1) the lower asthenosphere and upper transition zone; (2) the Upper Mantle/Lower Mantle (UM/LM) boundary region and the uppermost LM. The inclusions from zone 1 are very largely majoritic garnets (with or without clinopyroxene) which indicate bulk compositions of eclogitic/metabasic affinity. The minerals from zone 2 include Ca-Si and Mg-Si perovskites and ferropericlase and are dominantly of metaperidotitic bulk composition, but include some possible metabasite assemblages. In many of these natural assemblages, the tetragonal almandine pyrope phase occurs rather than the garnet found in experiments. As natural diamonds are believed to crystallize in fluids/melts, the hypothesis is developed that the restriction of diamonds and inclusions of particular compositions to the above two depth intervals is because they are controlled by loci of fluid/melt occurrence. Attention is focused on subduction zones because both suites of inclusions show some evidence of subducted protoliths. The lower zone (600800 km) coincides with the region where dehydration may be expected for hydrous ringwoodite and dense hydrous Mg-silicates formed in subducted peridotites. The dehydration of lawsonite in subducted metabasites provides a particular location for melt formation and the inclusion of the shallower (~300 km) majoritic inclusions. For the deeper majoritic inclusions in the region of the upper transition zone, melt development may occur as a consequence of the hydrous wadsleyite-to-olivine transformation, and such melt may then interact with the upper crustal portion of a subducting slab. These suggestions offer an explanation of the depth restrictions and the compositional restrictions of the inclusions. The differences in d 13 C values in the host diamonds for the two suites of inclusions may also be explained on this basis.

Alunite supergroup: recommended nomenclature

Abstract: Minamiite has been discredited and renamed natroalunite-2 c to show a double unit-cell structure and natroalunite can be designated as natroalunite-1 c to show a single unit-cell structure. Kintoreite can be designated as kintoreite-1 c to show the same single unit-cell structure, and IMA 1993-039 is a new superstructure of kintoreite and can be designated as kintoreite-2 c to show a double unit-cell structure. Beaverite has been renamed beaverite-(Cu). The Zn-bearing beaverite of Sato et al. (2008) has been named “beaverite-(Zn)”, but data for the mineral have not been approved by the CNMNC. Orpheite has been discredited as P-rich hinsdalite. Proposal 07-D was approved by the CNMNC.

The structure of charoite, (K,Sr,Ba,Mn)15–16(Ca,Na)32[(Si70(O,OH)180)](OH,F)4.0·nH2O, solved by conventional and automated electron diffraction

Abstract: Charoite, ideally (K,Sr,Ba,Mn)(15-16)(Ca,Na)(32)[(Si(70)(O,OH)(180))](OH,F)(4.0)center dot nH(2)O, a rare mineral from the Murun massif in Yakutiya, Russia, was studied using high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray spectroscopy, precession electron diffraction and the newly developed technique of automated electron-diffraction tomography. The structure of charoite (a = 31.96(6) angstrom, b = 19.64(4) angstrom, c = 7.09(1) angstrom, beta = 90.0(1)degrees, V = 4450(24) angstrom(3), space group P2(1)/m) was solved ab initio by direct methods from 2878 unique observed reflections and refined to R(1)/wR(2) = 0.17/0.21. The structure can be visualized as being composed of three different dreier silicate chains: a double dreier chain, [Si(6)O(17)](10-); a tubular loop-branched dreier triple chain, [Si(12)O(30)](12-); and a tubular hybrid dreier quadruple chain, [Si(17)O(43)](18-). The silicate chains occur between ribbons of edge-sharing Ca and Na-octahedra. The chains of tetrahedra and the ribbons of octahedra extend parallel to the z axis. K(+), Ba(2+), Sr(2+), Mn(2+) and H(2)O molecules lie inside tubes and channels of the structure. On the basis of microprobe analyses and occupancy refinement of the cation sites, the crystal chemical formula of this charoite can be written as (Z = 1): (K(13.88)Sr(1.0)Ba(0.32)Mn(0.36))(Sigma 15.56)(Ca(25.64)Na(6.36))Sigma 32 [(Si(6)O(11)(O,OH)(6))(2)(Si(12)O(18)(O,OH)(12))(2)(Si(17)O(25)(O,OH)(18 ))(2)](OH,F)(4.0)center dot 3.18H(2)O.

Primary and secondary phases in copper-cobalt smelting slags from the Copperbelt Province, Zambia

Abstract: Pyrometallurgical slags from three Cu-Co smelters (Nkana, Mufulira, Chambishi) in the Copperbelt Province, Zambia, were studied from mineralogical and chemical points of view. The slags were enriched in metals and metalloids, mainly Cu (up to 35 wt.%), Co (up to 2.4 wt.%) and As (up to 3650 ppm). The following primary phases were observed in slags: Ca-Fe silicates (clinopyroxene, olivine) and leucite, oxides (spinel-series phases), ubiquitous silicate glass and sulphide/metallic droplets of various sizes. The presence of glass and skeletal/dendritic crystal shapes indicated rapid cooling of the slag melt. Copper and cobalt were found in low concentrations in the majority of silicates (olivine, clinopyroxene) and oxides, substituting for Fe in their structures (up to 7.15 wt.% CoO in olivine, 4.11 wt.% CuO in spinel). Similarly, up to 0.91 wt.% CoO and 6.90 wt.% CuO were observed in the interstitial glass. Nevertheless, the main carriers of these metals in the slags studied were Cu sulphides (digenite, chalcocite, bornite, chalcopyrite), Co-Fe sulphides (cobaltpentlandite), Co-bearing intermetallic phases ((Fe,Co)2As) and alloys. Weathering features corresponding to the presence of secondary metal-bearing phases, such as malachite (Cu2(CO3)(OH)2), brochantite (Cu4SO4(OH)6) and sphaerocobaltite (CoCO3), were observed on the slag surfaces. They indicate that the slags studied are reactive on contact with water/atmosphere and that their environmental stability and release of potentially harmful metals and metalloids must be evaluated further.

Transmission electron microscopy (TEM) of Earth and planetary materials: A review

Abstract: Using high intensity beams of fast electrons, the transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) enable comprehensive characterization of rocks and minerals at micrometre to sub-nanometre scales. This review outlines the ways in which samples of Earth and planetary materials can be rendered sufficiently thin for TEM and STEM work, and highlights the significant advances in site-specific preparation enabled by the focused ion beam (FIB) technique. Descriptions of the various modes of TEM and STEM imaging, electron diffraction and X-ray and electron spectroscopy are outlined, with an emphasis on new technologies that are of particular relevance to geoscientists. These include atomic-resolution Z-contrast imaging by high-angle annular dark-field STEM, electron crystallography by precession electron diffraction, spectrum mapping using X-rays and electrons, chemical imaging by energy-filtered TEM and true atomic-resolution imaging with the new generation of aberration-corrected microscopes. Despite the sophistication of modern instruments, the spatial resolution of imaging, diffraction and X-ray and electron spectroscopy work on many natural materials is likely to remain limited by structural and chemical damage to the thin samples during TEM and STEM.

Mechanism of formation of atoll garnet during high-pressure metamorphism

Abstract: Atoll garnet has been found in metabasites and quartz- and mica-rich rocks that have experienced low- to medium-temperature, high-pressure eclogite facies metamorphism in the Krusne Hory (Erzgebirge). They occur in several localities but are restricted to thin, texturally distinct zones, even on a thin-section scale. The mechanism of atoll garnet formation is documented by a series of micrographs and compositional maps and profiles of atoll garnet in combination with textural relations to other phases in the rocks. The core of full garnet or its relics in the atoll garnet have larger Ca and Fe, but smaller Mg contents, compared with the thin rim (ring). In addition to quartz, Na-Ca amphibole and phengite, the atoll cores are filled by a new garnet that has a composition similar to the outer rim. Formation of the atoll garnet is interpreted as resulting from fluid infiltration and element exchange between the garnet core and matrix, a process facilitated by a temperature increase during eclogite facies metamorphism. In addition to fluid access, the primary textures, mainly grain size, were also effective for the atoll garnet formation. Small grain fractions with thin rims were easily infiltrated by fluid, which used the short distance for element exchange between core and matrix. The core garnet was gradually dissolved and replaced by new garnet having the same crystallographic orientation as the rim or relics in the core.

The experimental replacement of ilmenite by rutile in HCl solutions

Abstract: To determine the mechanism of acid-leaching of ilmenite to ultimately forming rutile, we have carried out an experimental study of ilmenite alteration in autoclaves at 150oC in HCl solutions. The resulting products were studied by X-ray diffraction, scanning electron microscopy, electron microprobe and Raman spectroscopy. In some experiments the solution was initially enriched in 18O and the distribution of the isotope in the alteration products mapped from the frequency shift of cation oxygen stretching bands in the Raman spectra. The alteration begins at the original ilmenite crystal surface and has also taken place along an intricate branching network of fractures in the ilmenite, generated by the reaction. Element-distribution maps and chemical analyses of the reaction product within the fractures show marked depletion in Fe and Mn and a relative enrichment of Ti. Chemical analyses however, do not correspond to any stoichiometric composition, and may represent mixtures of TiO2 and Fe2O3. The fracturing is possibly driven by volume changes associated with dissolution of ilmenite and simultaneous reprecipitation of the product phases (including rutile) from an interfacial solution along an inward moving dissolution-reprecipitation front. Raman spectroscopy shows that the 18O is incorporated in the rutile structure during the recrystallization. Throughout the alteration process, the original morphology of the ilmenite is preserved although the product is highly porous. The rutile inherits crystallographic information from the parent ilmenite, resulting in a triply-twinned rutile microstructure. The results indicate that the ilmenite is replaced directly by rutile without the formation of any intermediate reaction products. The reaction is described in terms of an interface-coupled dissolution-precipitation mechanism.

Fluid-mineral interactions and constraints on monazite alteration during metamorphism

Abstract: Clasts of metamorphosed Cadomian granites from the ∼50–60 Ma Carpathian flysch in Grodek near the Roznowskie Lake (Silesian Unit, SE Poland) are studied. They are considered to represent the Silesian Ridge, one of the hypothetical, currently unexposed source areas that supplied Carpathian sedimentary basins with clastic material. The gneisses preserve several examples of corona textures that include cores of primary monazite surrounded by polygonal grains of secondary apatite with thorianite inclusions, with intermediate zones of lamellar grains of secondary monazite and outermost rims of clay minerals, or various combinations thereof. Preservation of the complete textures is rare with polygonal apatite with thorianite inclusions, lamellar grains of monazite and clay minerals being particularly prevalent. Locally, polygonal apatite with thorianite inclusions surrounded by allanite and REE -epidote corona with a bastnasite-synchysite phase occurs also. The textures observed developed during primary monazite breakdown and replacement by secondary minerals. The variation in reaction products indicates that alteration was strictly dependent on the local chemical system.

Feldspars defined and described: a pair of posters published by the Mineralogical Society. Sources and supporting information

Abstract: The Mineralogical Society of Great Britain & Ireland has published two full-colour posters describing the feldspar minerals, designed primarily for student use. They may be downloaded free of charge by all from http://www.minersoc.org/pages/education/edu.html and are designed to be printed at A3 size, although they are legible at A4 and in greyscale. Sheet 1 deals with nomenclature, crystal structure and phase relationships, while Sheet 2 covers phase behaviour. For brevity no sources are given on the posters, and these are provided in the present article, together with supporting notes and suggested reading on the more complex topics.

Compositional variation of the tennantite–tetrahedrite solid-solution series in the Schwarzwald ore district (SW Germany): The role of mineralization processes and fluid source

Abstract: The study presents analysis from members of the tennantite–tetrahedrite solid-solution series (‘fahlore’) from 78 locations in the Schwarzwald ore district of SW Germany. Electron microprobe analysis is used to correlate the compositional variations of the fahlores with mineral association, host rock, tectonic history and precipitation mechanisms. Results indicate that most fahlores from gneiss-hosted veins do not have distinctive geochemical characteristics and range from tetrahedrite to tennantite end-member composition with variable trace-element content. However, diagenetically formed fahlore has a near-end-member tennantite composition with very small trace-element content. Red-bed-hosted fahlore formed by fluid mixing is tennantite enriched in Hg that probably has its source in the red-bed sediments. Fahlore formed from granite-related late-magmatic fluids, or from mixing of fluids of which one has equilibrated with granitic basement rocks, is typically As- and Bi-rich (up to 22.2 wt.% Bi). Gneiss-hosted fahlore formed by fluid cooling is Ag-rich near-end-member tetrahedrite. Some fahlores reflect their paragenetic association, e.g. a large Ag content in association with Ag-bearing minerals or a large Co and Ni in association with Co- and Ni-arsenides. Although they have similar compositions, gneiss-hosted fahlores show systematic variations in Ag contents and Fe/Zn ratios between the Central and the Southern Schwarzwald with Fe-rich fahlore in higher stratigraphic levels (North) and Zn- and Ag-rich fahlore in lower stratigraphic levels (South). We show that fahlore composition varies with precipitation mechanism (cooling vs. mixing vs. diagenesis), depth of formation, paragenetic association and host rock. Comparison with fahlores from other European occurrences indicates that these conclusions are consistent with fahlore systematics found elsewhere, and could be used to infer details of ore-forming processes.

The electrical conductivity of dry polycrystalline olivine compacts at high temperatures and pressures

Abstract: The electrical conductivity of dry polycrystalline olivine compacts (hot-pressed and sintered pellets) was measured at pressures of 1.0–4.0 GPa, at temperatures of 1073–1423 K, and at different oxygen fugacities via the use of a YJ-3000t multi-anvil press. Oxygen fugacity was controlled successfully by means of five solid buffers: Fe 3 O 4 -Fe 2 O 3 , Ni-NiO, Fe-Fe 3 O 4 , Fe-FeO and Mo-MoO 2 . Within the selected frequency range of 10 2 –10 6 Hz, the experimental results indicate that the grain interior conduction mechanism is characterized by a semi-circular curve on an impedance diagram. As a function of increasing pressure, the electrical conductivity of polycrystalline olivine compacts decreases, whereas the activation enthalpy and the temperature-independent pre-exponential factors increase slightly. The activation energy and activation volume of polycrystalline olivine compacts were determined to be 141.02±2.53 kJ/mol and 0.25±0.05 cm 3 /mol, respectively. At a pressure of 4.0 GPa, electrical conductivity was observed to increase as a function of increasing oxygen fugacity, and the relationship between electrical conductivity and oxygen fugacity can be described as log 10 (σ) = (2.47±0.085) + (0.096±0.023)×log 10 f O 2 +(−0.55±0.011)/ T , which presents the exponential factor q (∼0.096). Our observations demonstrate that the primary conduction mechanism for polycrystalline olivine compacts is a small polaron.

Crystal chemistry of natural layered double hydroxides. 3. The crystal structure of Mg,Al-disordered quintinite-2H

Abstract: Two crystals of Mg,Al-disordered quintinite-2 H (Q1 and Q2), [Mg4Al2(OH)12](CO3)(H2O)3, from the Kovdor alkaline massif, Kola peninsula, Russia, have been characterized chemically and structurally. Both crystals have hexagonal symmetry, P 63/ mcm , a = 3.0455(10)/3.0446(9), c = 15.125(7)/15.178(5) A, V = 121.49(8)/121.84(6) A3. The structures of the two crystals have been solved by direct methods and refined to R1 = 0.046 and 0.035 on the basis of 76 and 82 unique observed reflections for Q1 and Q2, respectively. Diffraction patterns obtained using an image-plate area detector showed the almost complete absence of superstructure reflections which would be indicative of the Mg-Al ordering in metal hydroxide layers, as has been observed recently for other quintinite polytypes. The crystal structures are based on double hydroxide layers [ M (OH)2] with an average disordered distribution of Mg2+ and Al3+ cations. Average bond lengths for the metal site are 2.017 and 2.020 A for Q1 and Q2, respectively, and are consistent with a highly Mg-Al disordered, average occupancy. The layer stacking sequence can be expressed as...=AC=CA=..., corresponding to a Mg-Al-disordered 2 H polytype of quintinite. The observed disorder is probably the result of a relatively high temperature of formation for the Q1 and Q2 crystals compared to ordered polytypes. This suggestion is in general agreement with the previous observations which demonstrated, for the Mg-Al system, a higher-temperature regime of formation of the hexagonal (or pseudo-hexagonal in the case of quintinite-2 H -3 c ) 2 H polytype in comparison to the rhombohedral (or pseudo-rhombohedral in the case of quintinite-1 M ) 3 R polytype.

Crystal chemistry of natural layered double hydroxides. I. Quintinite-2H-3c from the Kovdor alkaline massif, Kola peninsula, Russia

Abstract: The crystal structure of quintinite-2 H -3 c , [Mg 4 Al 2 (OH) 12 ](CO 3 )(H 2 O) 3 , from the Kovdor alkaline massif, Kola peninsula, Russia, was solved by direct methods and refined to an agreement index ( R 1 ) of 0.055 for 484 unique reflections with | F o | ≥ 4σ F . The mineral is rhombohedral, R 32, a = 5.2745(7), c = 45.36(1) A. The diffraction pattern of the crystal has strong and sharp Bragg reflections having h – k = 3 n and l = 3 n and lines of weak superstructure reflections extended parallel to c * and centred at h – k ≠ 3 n . The structure contains six layers within the unit cell with the layer stacking sequence of...AC=CA=AC=CA=AC=CA... The Mg and Al atoms are ordered in metal hydroxide layers to form a honeycomb superstructure. The full superstructure is formed by the combination of two-layer stacking sequence and Mg-Al ordering. This is the first time that a long-range superstructure in carbonate-bearing layered double hydroxide (LDH) has been observed. Taking into account Mg-Al ordering, the unique layer sequence can be written as...=Ab 1 C=Cb 1 A=Ab 2 C=Cb 2 A=Ab 3 C=Cb 3 A=... The use of an additional suffix is proposed in order to distinguish between LDH polytypes having the same general stacking sequence but with different c parameters compared with the `standard9 polytype. According to this notation, the quintinite studied here can be described as quintinite-2 H -3 c or quintinite-2 H -3 c [6 R ], indicating the real symmetry.

The synthesis and solubility of the copper hydroxyl nitrates: gerhardtite, rouaite and likasite

Abstract: Syntheses for the three members of the copper hydroxyl nitrate family – the polymorphs rouaite and gerhardtite, and likasite – are presented along with powder diffraction data and unit-cell parameters. The solubilities, determined in 0.05 m KNO3 solution after equilibration at 25°C for 10 days were used to calculate activity-based solubility product constants. The Gibbs energies of formation, obtained from the solubility products, are −653.2±0.7 kJ/mol, −655.1±1.2 kJ/mol and −1506.4±1.1 kJ/mol, for rouaite, gerhardtite, and likasite (Cu3NO3(OH)5·2H2O), respectively. The values for the polymorphs rouaite and gerhardtite validate the observations of Oswald that gerhardtite is the most stable polymorph at room temperature and that the preparation of predominantly rouaite in syntheses carried out at room temperature must be due to the metastability and low rate of conversion to the more stable gerhardtite.

Octahedrally coordinated vacancies in tourmaline: a theoretical approach

Abstract: Bond-valence theory is used to explore the local arrangements involving vacancies at the Y and Z sites in the tourmaline structure. The local bond-valence requirements of all possible local arrangements around the O8, O7, O6, O3 and O1 anion-sites have been determined for Y - and Z -site vacancies locally associated with Li 1+ , Mg 2+ , Al 3+ , Fe 2+ , Fe 3+ , B 3+ and Si 4+ . The results show that arrangements involving tetrahedrally coordinated T R 3+ -cations and octahedrally coordinated Y R 2+ - and Z R 2+ -cations around O8, O7 and O6 can be ruled out, together with arrangements involving vacancies and Y Li 1+ . As the occurrence of a Y -site vacancy ( Y □) is more in accord with the valence-sum rule than the occurrence of a Z -site vacancy ( Z □), Y □ is more likely to occur than Z □ in tourmaline. Local arrangements involving vacancies around O1- and O3-sites can be stable for OH − , but not for O 2− . Of particular interest in this regard are the arrangements [ Y R 3+ Y R 3+ Y □]– O1 (OH − ) and [ Z R 3+ Z R 3+ Y □]– O3 (OH − ), which yield the smallest deviations from the valence-sum rule. Coupling these stable arrangements with 2 × [ T Si 4+ Z R 3+ Y □]– O6 (O 2− ) forms larger vacancy clusters: [ Y ( R 3+ ) 2 – O1 (OH − )– Y (□)– O3 (OH − )– O6 (O 2− ) 2 –( Z R 3+ T Si 4+ ) 2 ]. In tourmaline, vacancies are more favoured to occur at Y rather than at Z , in tandem with OH − at O3 and O1, R 3+ at Y and Z and Si 4+ at T .

Demicheleite-(I), BiSI, a new mineral from La Fossa Crater, Vulcano, Aeolian Islands, Italy

Abstract: Demicheleite-(I), ideally BiSI, is the iodine-dominant analogue of demicheleite-(Br) and demicheleite-(Cl). It was found in an active medium-temperature intracrateric fumarole at La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. The mineral is the first bismuth sulphoiodide so far discovered in a wholly natural environment, and corresponds to the already known synthetic compound. It occurs as acicular to stout, translucent crystals up to 0.25 mm long in an altered pyroclastic breccia, together with demicheleite-(Br), bismoclite, bismuthinite, godovikovite, panichiite, aiolosite, brontesite, adranosite and other new phases under study. The colour is dark red to black, the lustre submetallic. The unit cell is orthorhombic, space group Pnam, with a = 8.4501(7) A, b = 10.1470(9) A , c = 4.1389(4) A , V = 354.88(4) A3, and Z = 4. The crystal habit is prismatic, with the main forms {110} and {111} inferred from analogy with demicheleite-(Br). Twinning was not observed. The strongest 6 lines in the X-ray powder diffraction pattern [d obs.(A) (I/I 0) (hkl)] are: 6.490 (100) (110); 4.346 (94) (120); 3.896 (90) (210); 2.709 (60) (310); 2.161 (38) (330); 3.243 (22) (220). The chemical analysis obtained by WDS electron microprobe gave: Bi 58.32, S 9.43, I 23.69, Br 5.66, Cl 1.01, totalling 98.11 wt.%, corresponding to an empirical formula (based on 3 a.p.f.u.) of: Bi0.97S1.03(I0.65Br0.25Cl0.10)Σ1.00. The unit-cell data are close to those of the synthetic compound, whose crystal structure is already known. The calculated density is 6.411 g cm–3.

Crystal chemistry of natural layered double hydroxides. 2. Quintinite-1M: first evidence of a monoclinic polytype in M2+-M3+ layered double hydroxides

Abstract: Quintinite-1 M , [Mg 4 Al 2 (OH) 12 ](CO 3 )(H 2 O) 3 , is the first monoclinic representative of both synthetic and natural layered double hydroxides (LDHs) based on octahedrally coordinated di- and trivalent metal cations. It occurs in hydrothermal veins in the Kovdor alkaline massif, Kola peninsula, Russia. The structure was solved by direct methods and refined to R 1 = 0.031 on the basis of 304 unique reflections. It is monoclinic, space group C 2/ m , a = 5.266(2), b = 9.114(2), c = 7.766(3) A, β = 103.17(3)°, V = 362.9(2) A 3 . The diffraction pattern of quintinite-1 M contains sharp reflections corresponding to the layer stacking sequence characteristic of the 3 R rhombohedral polytype, and rows of weak superlattice reflections superimposed upon a background of streaks of modulated diffuse intensity parallel to c * . These superlattice reflections indicate the formation of a 2-D superstructure due to Mg-Al ordering. The structure consists of ordered metal hydroxide layers and a disordered interlayer. As the unit cell contains exactly one layer, the polytype nomenclature dictates that the mineral be called quintinite-1 M . The complete layer stacking sequence can be described as...=Ac 1 B=Ba 1 C=Cb 1 A=... Quintinite-1 M is isostructural with the monoclinic polytype of [Li 2 Al 4 (OH) 12 ](CO 3 )(H 2 O) 3 .

Kirschsteinite in the Capo di Bove melilite leucitite lava (cecilite), Alban Hills, Italy

Abstract: Kirschsteinite (mainly CaFeSiO4), in association with forsterite-fayalite solid solutions, melilite, clinopyroxene, leucite, nepheline and several minor phases, is reported for the first time in the 290 ka Capo di Bove melilite-leucitite lava flow of the Alban Hills volcanic complex (Italy). Kirschsteinite appears very late in the crystallization sequence, as indicated by textural and chemical evidence (Mg# ≈ 25). It shows significant solid solution towards fayalite, and is found with groundmass phases indicating a relatively low-temperature melt composition more silica-undersaturated than phonolite (i.e. devoid of alkali feldspar). This clearly points to the very silica-undersaturated nature of almost all the Alban Hills volcanic rocks.

Atomic scale models of dislocation cores in minerals: progress and prospects

Abstract: Recent advances in computer simulation at the atomic scale have made it possible to probe the structure and behaviour of the cores of dislocations in minerals. Such simulation offers the possibility to understand and predict the dislocation-mediated properties of minerals such as mechanisms of plastic deformation, pipe diffusion and crystal growth. In this review the three major methods available for the simulation of dislocation cores are described and compared. The methods are: (1) cluster-based models which combine continuum elastic theory of the extended crystal with an atomistic model of the core; (2) dipole models which seek to cancel the long-range elastic displacement caused by the dislocation by arranging for the simulation to contain several dislocations with zero net Burgers vector, thus allowing a fully periodic super-cell calculation; and (3) the Peierls-Nabarro approach which attempts to recast the problem so that it can be solved using only continuum-based methods, but parameterizes the model using results from atomic-scale calculations. The strengths of these methods are compared and illustrated by some of the recent studies of dislocations in mantle silicate minerals. Some of the unresolved problems in the field are discussed.

Rare earth element geochemistry of columbite-group minerals: LA-ICP-MS data

Abstract: New data on rare earth element (REE) concentrations and distribution patterns of columbite-tantalite minerals from Ta-ore provinces worldwide are presented. The REE geochemistry was studied by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Five major types of chondrite-normalized REE distribution patterns are defined for columbite-group minerals (CGM) from lithium-caesium-tantalum (LCT) pegmatites and rare-metal granites. Features to discriminate between the types include (1) the shape of the pattern (e.g. flat or concave), (2) calculated ratios between groups of the REE (e.g. heavy REE N/middle REE N), and (3) the presence and intensity of anomalies (e.g. Ce*, Eu*). Four pegmatites in central and southern Africa are used as case studies to discuss application of the types of REE patterns in individual deposits. The REE fractionation during progressive evolution of the melt in a pegmatite body (either Nb → Ta or Fe → Mn fractionation lines, or both) results in smaller heavy REE N/middle REE N ratios whereas replacement of primary CGM by secondary CGM produces modifications in the light REE N patterns and the heavy REE N/middle REE N ratios also. Critical features of REE patterns such as highly variable heavy REE N/middle REE N ratios or striking differences in the appearance of Eu anomalies are discussed considering structural data of the host minerals and the differentiation behaviour of the pegmatitic melt. In general, CGM from each individual Ta-ore province are characterized by a predominance of one type of REE distribution pattern. Consequently, these patterns are suitable for tracing the origin of tantalum ore concentrates (e.g. as a forensic tool).

IMA Commission on New Minerals, Nomenclature and Classification (CNMNC)

Abstract: P. A. WILLIAMS (Chairman, CNMNC), F. HATERT (Vice-Chairman, CNMNC), M. PASERO (Vice-Chairman, CNMNC) AND S. J. MILLS (Secretary, CNMNC) 1 School of Science and Health, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australia p.williams@uws.edu.au 2 Laboratoire de Mineralogie, Universite de Liege, B-4000 Liege, Belgium fhatert@ulg.ac.be 3 Dipartimento di Scienze della Terra, Universita degli Studi di Pisa, Via Santa Maria 53, I-56126 Pisa, Italy marco.pasero@dst.unipi.it 4 Geosciences, Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia smills@museum.vic.gov.au

The decomposition of konyaite: importance in CO2 fixation in mine tailings

Abstract: The sodium-magnesium hydrated double salt konyaite, Na 2 Mg(SO 4 ) 2 ·5H 2 O, has been studied by single-crystal X-ray diffraction and thermogravimetry on synthetic samples and by quantitative X-ray diffraction utilizing the Rietveld method on natural samples from the Mount Keith mine, Western Australia. Konyaite crystallizes in space group P 2 1 / c , with the cell parameters: a = 5.7594(10), b = 23.914(4), c = 8.0250(13) A, β = 95.288(9)°, V = 1100.6(3) A 3 and Z = 4. The crystal structure has been refined to R 1 = 3.41% for 2155 reflections [F o >4σ(F o )] and 6.44% for all 3061 reflections, with all atoms located. Quantitative phase analysis utilizing the Rietveld method was undertaken on five samples of konyaite-bearing mine tailings from the Mount Keith Nickel Mine, Western Australia. Konyaite was found to decompose over time and after 22 months had transformed to other sulphate and amorphous phases. Blodite did not increase in any of the samples indicating that konyaite may not always transform to blodite. Over the same time frame, synthetic konyaite completely decomposed to a mixture of thenardite (Na 2 SO 4 ), hexahydrite (MgSO 4 ·6H 2 O), blodite (Na 2 Mg(SO 4 ) 2 ·4H 2 O) and loweite (Na 12 Mg 7 (SO 4 ) 13 ). Detection of konyaite and other Mg-rich sulphates is important in terms of CO 2 fixation. Magnesium bound to sulphate mineral phases reduces the overall potential of tailings piles to lock up atmospheric carbon in Mg carbonates, such as hydromagnesite. Amorphous sulphates are also highly reactive and may contribute to acid mine drainage if present in large quantities, and may dissolve carbonate phases which have already sequestered carbon.

Jahnsite–whiteite solid solutions and associated minerals in the phosphate pegmatite at Hagendorf-Süd, Bavaria, Germany

Abstract: Secondary phosphate assemblages from the Hagendorf Sud granitic pegmatite, containing the new Mn-Al phosphate mineral, nordgauite, have been characterized using scanning electron microscopy and electron microprobe analysis Nordgauite nodules enclose crystals of the jahnsite–whiteite group of minerals, showing pronounced compositional zoning, spanning the full range of Fe/Al ratios between jahnsite and whiteite The whiteite-rich members are F-bearing, whereas the jahnsite-rich members contain no F Associated minerals include sphalerite, apatite, parascholzite, zwieselite-triplite solid solutions and a kingsmountite-related mineral The average compositions of whiteite and jahnsite from different zoned regions correspond to jahnsite-(CaMnMn), whiteite-(CaMnMn) and the previously undescribed whiteite-(CaMnFe) end-members Mo- K α CCD intensity data were collected on a twinned crystal of the (CaMnMn)-dominant whiteite and refined in P 2/ a to wR obs = 0064 for 1015 observed reflections

A temperature-dependent structure study of gem-quality hibonite from Myanmar

Abstract: The structure of hibonite from Myanmar (space group P 6 3 / mmc , Z = 2, at room temperature a = 5.5909(1), c = 21.9893(4)A), with simplified formula CaAl 12 O 19 and composition (Ca 0.99 Na 0.01 ) Σ1.00 (Al 10.74 Ti 0.52 Mg 0.51 Zn 0.11 Si 0.08 \(\mathrm{Fe}_{0.04}^{2+}\) ) Σ12.00 O 18.97 , was investigated between temperatures of 100 K and 923 K by single-crystal X-ray diffraction methods. Structure refinements have been performed at 100, 296, 473 and 923 K. In hibonite from Myanmar, Ti substitutes for Al mainly at the octahedral Al4 site and, to a lesser degree, at the trigonal bipyramidal site, Al2. The Al4 octahedra build face-sharing dimers. If Ti 4+ substitutes at Al4, adjacent cations repulse each other for electrostatic reasons, leading to off-centre cation displacement associated with significant bond-length distortion compared to synthetic (Ti-free) CaAl 12 O 19 . Most Mg and smaller proportions of Zn and Si are assigned to the tetrahedral Al3 site. 12-coordinated Ca in hibonite replaces oxygen in a closest-packed layer. However, Ca is actually too small for this site and engages in a `rattling-type9 motion with increasing temperature. For this reason, Ca does not significantly increase thermal expansion coefficients of hibonite. The expansion of natural Ti,Mg-rich hibonite between 296 and 923 K along the x and the z axes is α a = 7.64 × 10 −6 K −1 and α c = 11.19 × 10 −6 K −1 , respectively, and is thus very similar to isotypic, synthetic CaAl 12 O 19 and LaMgAl 11 O 19 (LMA).

Minerals of the ammonioalunite–ammoniojarosite series formed on a burning coal dump at Czerwionka, Upper Silesian Coal Basin, Poland

Abstract: Ammonioalunite, ammoniojarosite and their solid-solution series found on a burning coal dump at Czerwionka, Upper Silesian Coal Basin, Poland, were examined using powder X-ray diffraction, electron probe microanalysis, inductively coupled plasma mass spectrometry, infrared spectroscopy and thermal analysis methods. The minerals occur as yellow, fine-grained crusts and botryoidal masses in the outer part of a sulphate crust found ∼1 m below the surface. The crust is composed mainly of godovikovite and tschermigite that formed by interaction of sour fire gases or solutions and waste materials beneath the surface of the burning coal dump at temperatures of at least 80–100°C. The crystals often reveal oscillatory zoning due to different Al and Fe contents in thin bands, from near end-members to extensive solid solutions. Our analyses suggest the existence in nature of a complete solid solution between ammonioalunite and ammoniojarosite. They also carry essential amounts of chlorine.

New minerals and nomenclature modifications approved in 2010

Abstract: The information given here is provided by the IMA Commission on New Minerals, Nomenclature and Classification for comparative purposes and as a service to mineralogists working on new species Each mineral is described in the following format: Mineral name, if the authors agree on its release prior to the full description appearing in press Chemical formula Type locality Full authorship of proposal E-mail address of corresponding author Relationship to other minerals Crystal system, Space group; Structure determined, yes or no Unit-cell parameters Strongest lines in the X-ray powder-diffraction pattern Type specimen repository and specimen number Citation details for the mineral prior to publication of full description It is still a requirement for the authors to publish a full description of the new mineral NO OTHER INFORMATION WILL BE RELEASED BY THE COMMISSION ### IMA No 2005-025a Afmite Al3(OH)4(H2O)3(PO4)(PO3OH)·H2O Fumade, Castelnau-de-Brassac, Tarn, France (43°39′30″N, 2°29′58″E) Anthony R Kampf*, Georges Favreau, Ian M Steele, Stuart J Mills, George R Rossman and Joseph J Pluth *Email: akampf@nhmorg Related to planerite and kobokoboite Triclinic: P![Formula][1] ; structure determined a = 7386(3), b = 7716(3), c = 11345(4) A, α = 99773(5), β = 91141(6), γ = 11558(5)° 11130(100), 6813(30), 5499(62), 4029(24), 3532(65), 3087(41), 2918(43), 2466(21) Type material is deposited in the Natural History Museum of Los Angeles County, Los Angeles, catalogue number 55425 How to cite: Kampf, AR, Favreau, G, Steele, IM, Mills, SJ, Rossman, GR and Pluth, JJ (2010) Afmite, IMA 2005-025a CNMNC Newsletter, August 2010, page 797; Mineralogical Magazine , 74 , 797–800 ### IMA No 2010-016 Cranswickite MgSO4·4H2O Small workings 1 km ESE of Calingasta, Argentina (31°20351′S 69 23546′W) Ronald C Peterson *E-mail: peterson@geolqueensuca New structure type; dimorphous with starkeyite; unnamed mineral UM1999-28-SO:HMg Monoclinic: Cc ; structure … [1]: /embed/tex-math-1gif

Elastic instabilities in dry, mesoporous minerals and their relevance to geological applications

Abstract: The collapse of minerals and mineral assemblies under external stress is modelled using a master curve where the stress failure is related to the relative, effective elastic moduli which are in turn related to the porosity of the sample. While a universal description is known not to be possible, we argue that for most porous materials such as shales, silica, cement phases, hydroxyapatite, zircon and also carbonates in corals and agglomerates we can estimate the critical porosity φc at which small stresses will lead to the collapse of the sample. For several samples we find φc ∼0.5 with an almost linear decay of the bulk moduli with porosity at φc 2, between φ = 0.5 and φ = 1.

Boron and lithium isotopic compositions as provenance indicators of Cu-bearing tourmalines

Abstract: The Li and B isotopic compositions of gem-quality Cu-bearing tourmalines were used (1) to distinguish among Paraiba tourmalines from Brazil and Cu-bearing tourmalines from Nigeria and Mozambique; and (2) to identify the likely source of Li and B for these gem-quality tourmalines. The δ 11 B values of tourmaline from Paraiba, Brazil, range from -42.4‰ to -32.9‰, whereas the δ 11 B values of Cu-bearing tourmaline from Nigeria and Mozambique range from -30.5‰ to -22.7‰ and -20.8‰ to -19.1‰ respectively. Tourmalines from each locality have relatively homogeneous δ 11 B values and display no overlap. There is slight overlap between δ 7 Li values of Paraiba tourmaline (+24.5‰ to +32.9‰) and Cu-bearing tourmaline from Nigeria (+32.4‰ to +35.4‰), and δ 7 Li values of Cu-bearing tourmaline from Nigeria and Mozambique (+31.5‰ to +46.8‰). Nevertheless, Cu-bearing tourmalines from each locality can be fingerprinted using a combination of their δ 11 B and δ 7 Li values. The very small δ 11 B values are consistent with a non-marine evaporite source, and are among the smallest reported for magmaticsystems, expanding the global range of B isotopic composition for tourmaline by 12‰. The corresponding large δ 7 Li values are among the largest reported, although they are less diagnosticof the source of the Li. The large δ 7 Li values in conjunction with the small δ 11 B values suggest a non-marine evaporite or brine as a source for Li and B, either as constituent(s) of the magma source region or, by assimilation during magma ascent. The large range in δ 11 B and δ 7 Li values suggests that B and Li isotope fractionation occurred during magmatic degassing and late-stage magmatic-hydrothermal evolution of the granite-pegmatite system.

The crystal structure of Mg end-member lizardite-1T forming polyhedral spheres from the Lizard, Cornwall

Abstract: The crystal structure of lizardite-1 T from Gew-graze, Cornwall, has been refined by single-crystal X-ray diffractionto R 1 of 0.0263 and 0.0557, for two crystals having P 31 m space group and lattice parameters a = 5.2905(5) A, c = 7.2815(8) A, and a = 5.3111(10) A, c = 7.2907(15) A, respectively. The Gew-graze lizardite is very close to the end-member composition, so these refinements confirm the existence of well crystallized pure Mg-lizardite and show this to be the most weakly H-bonded lizardite ever refined. With regard to its lattice parameters, Si–O bond distances and geometrical parameters controlled by interlayer interactions (i.e. H-bonding), the Gew-graze Mg end-member lizardite yields slight but observable geometrical differences compared with previous refined structures for specifically, aluminous, lizardites.

Evolution of nepheline from mafic to highly differentiated members of the alkaline series: the Messum complex, Namibia

Abstract: The change in chemical composition trend of magmatic nepheline through magma evolution has been characterized from the alkaline series of the Messum complex in which nepheline occurs in a succession of different mineral parageneses from mafic-rich (theralites) to strongly evolved felsic-rich rock types (nepheline syenites). The nepheline compositions are dependent on those of coexisting feldspar(s). They record an evolution parallel to that of the melt schematized according to experimental phase diagrams, from initially Ca-rich compositions in equilibrium with calcic plagioclase towards increasingly Ca-poor, Na-rich and Si-rich compositions. The K contents show a maximum that corresponds to the appearance of alkali feldspar in the parageneses. This evolution is qualitatively preserved in spite of the low-T Na/K re-equilibration typical of plutonic nephelines. Although a slight increase in the silica content of nepheline is consistent with the experimentally defined magmatic trend, several high-silica nephelines from the Messum rocks as well as from other reported occurrences, cannot be reconciled with the experimental data. The nepheline solid-solution model available suggests that such ‘abnormal’ compositions might be related to different crystallization mechanisms between natural nephelines and some synthetic analogues.