Tabular Habit Research Articles

Authigenic Barite in Tailing Dumps: Mineralogical and Geochemical Data and Results of Physico-Chemical Modeling

On the example of the Novo-Ursk tailing dump (Salair Ridge), the typomorphic characteristics of barite are considered. It was found that in the dumps, in addition to residual barite from pyrite-polymetallic ores, there are its authigenic varieties. Ore barite grains are found in the form of fragments of irregular shapes, less often grains of a tabular habit, have a dimension of 50–400 microns, Sr up to 1.41 wt.%. Newly formed barite occurs as single grains or clusters of round and elongated shapes or acicular crystals, ranging in size from 1–2 µm to larger aggregates that form veinlets or clusters in the siliceous matrix in association with jarosite and/or anhydrite. Among the impurities, Pb up to 6.33 wt.% was noted, less often Fe up to 0.73 wt.%, Sr up to 0.94 wt.%. It was shown by using thermodynamic modeling that the concentrations of Ba, SO4, Fe and Ca in solution vary within several orders of magnitude when the mineral composition of the tailings mound zones changes depending on the Eh–pH conditions of their formation. It has been suggested that the formation of barite along with pyrite may occur as a result of the action of a reductive biogeochemical barrier or a sulfate concentration barrier in the deeper parts of the section where supersaturation is achieved.The most informative typomorphic feature proving that barite was formed under tailings conditions is particle morphology, mineral association and chemical composition.

Variation of plagioclase shape with size in intermediate magmas: a window into incipient plagioclase crystallisation

Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ascent to the surface. While variations in mineral compositions, sizes and number densities are routinely analysed to reconstruct pre-eruptive magmatic histories, crystal shapes are often assumed to be constant, despite experimental evidence for the sensitivity of crystal habit to magmatic conditions. Here, we develop a new program (ShapeCalc) to calculate 3D shapes from 2D crystal intersection data and apply it to study variations of crystal shape with size for plagioclase microlites (l < 100 µm) in intermediate volcanic rocks. The smallest crystals tend to exhibit prismatic 3D shapes, whereas larger crystals (l > 5–10 µm) show progressively more tabular habits. Crystal growth modelling and experimental constraints indicate that this trend reflects shape evolution during plagioclase growth, with initial growth as prismatic rods and subsequent preferential overgrowth of the intermediate dimension to form tabular shapes. Because overgrowth of very small crystals can strongly affect the external morphology, plagioclase microlite shapes are dependent on the available growth volume per crystal, which decreases during decompression-driven crystallisation as crystal number density increases. Our proposed growth model suggests that the range of crystal shapes developed in a magma is controlled by the temporal evolution of undercooling and total crystal numbers, i.e., distinct cooling/decompression paths. For example, in cases of slow to moderate magma ascent rates and quasi-continuous nucleation, early-formed crystals grow larger and develop tabular shapes, whereas late-stage nucleation produces smaller, prismatic crystals. In contrast, rapid magma ascent may suppress nucleation entirely or, if stalled at shallow depth, may produce a single nucleation burst associated with tabular crystal shapes. Such variation in crystal shapes have diagnostic value and are also an important factor to consider when constructing CSDs and models involving magma rheology.

Ultrathin DDR Films with Exceptionally High CO2 Flux and Uniformly Adjustable Orientations

AbstractThin and oriented zeolite films are important for advanced separations, catalysis, and sensing. Strategies for tailoring zeolites for applications include controlling their crystal size, shape, and orientation. Here, three siliceous DDR zeolite ultrathin films with different orientations achieved by homoepitaxial growth from 60 nm‐sized seed particles are reported. The 0.5 µm thick membrane shows a separation selectivity of 400 for CO2–CH4 mixtures and CO2 permeance of 25 × 10‐7 mol m‐2 s‐1 Pa‐1 at 20 °C and 1 bar, leading to a record‐high performance among all reported DDR membranes. Furthermore, the seed nanoparticles are grown into mono‐dispersed DDR sub‐micron crystals with trigonal and tabular habits. These crystals are assembled in monolayers for the growth of ultrathin and uniformly (h0h)‐oriented and c‐oriented films with maximum surface pore diameter of 0.365 and 0.263 nm, respectively, by using the 1‐adamantanamine template in fluoride medium. The novel strategy not only provides high‐performance membrane candidates for industrial CO2 separation, but also inspires interfacial engineering, pore size, and orientation controlling for other microporous crystals, and their membranes.

Mineralogical classification and crystal water characterisation of beryl from the W–Sn–Be occurrence of Xuebaoding, Sichuan province, western China

AbstractBeryl from Xuebaoding, Sichuan Province, western China is known for its unusual tabular habit and W–Sn–Be paragenesis in a greisen-type deposit. The crystals are typically colourless transparent to pale blue, often with screw dislocations of hexagonal symmetry on the (0001) crystal faces. Combining electron microprobe analyses and laser ablation inductively coupled plasma mass spectrometry with single-crystal X-ray diffraction (XRD), correlated with Raman and micro-infrared (IR) spectroscopy and imaging, the crystal chemical characteristics are determined. The contents of Na+ (0.24–0.38 atoms per formula unit (apfu)) and Li+ up to 0.38 apfu are at the high end compared to beryl from other localities worldwide. Li+ substitution for Be2+ on the tetrahedral (T2) site is predominantly charge balanced by Na+ on the smaller channel (C2) site, with Na+ ranging from 91.5% to 99.7% (apfu) of the sum of all other alkali elements. Cs+ and minor Rb+ and K+ primarily charge balance the minor M2+ substitution for Al3+ at the A site; all iron at the A site is suggested to be trivalent. The a axis ranges from 9.2161(2) to 9.2171(4) Å, with unit-cell volume from 678.03(3) to 678.48(7) Å3. The c/a ratio of 1.0002–1.0005 is characteristic for T2-type beryl with unit-cell parameters controlled primarily by Be2+ substitution. Transmission micro-IR vibrational spectroscopy and imaging identifies coordination of one or two water molecules to Na+ (type IIs and type IId, respectively) as well as alkali free water (type I). Based on IR absorption cross section and XRD a C1 site water content of 0.4–0.5 apfu is derived, i.e. close to 50% site occupancy. Secondary crystal phases with a decrease in Fe and Mg, yet increase in Na, suggest early crystallisation of aquamarine, with goshenite being late. With similar crystal chemistry to beryl of columnar habit from other localities worldwide, the tabular habit of Xuebaoding beryl seems to be unrelated to chemical composition and alkali content.

Morphological Characterization of Indoor Airborne Particles in Seven Primary Schools.

This paper focuses on a study of fine (less than 2.5 µm) airborne particles collected inside seven primary schools located on a coastal Mediterranean area which has a significant industrial hub for the processing of clays and other minerals as raw materials. Of the seven schools, three are located in an urban area 20 km away from the main industrial hub, three are in a town located next to the industrial estate, and one is in a rural location, 30 km from the industrial area. The objective of this study is to identify the main types of particles found in the three examined environments. The particle matter identified in the fine particle samples is grouped into three main groups: mineral compounds, particles from combustion processes and phases emitted in high-temperature industrial processes. The mineral particles, which can come from natural or anthropogenic emissions, have been classified depending on their morphology as isometric allotriomorphs or subidiomorphs, with a tabular habit; acicular forms; or pure crystalline forms. Compounds from combustion processes have two types of morphologies: spheroid and dendritic soot particles. Additionally, in smaller quantities, spherical particles associated with high-temperature industrial processes, such as the emissions of ceramic tile-firing and frit-melting processes, are identified. A summary table is shown, which lists the characteristics, as well as the most significant origin of the main particles identified in the fine (<2.5 μm) airborne particles collected inside primary schools located in three different environments (urban, industrial and rural). A visual scale has been established based on the number of particles observed in the samples of the atmospheric particulate fraction between the sizes of 2.5 and 10 µm collected inside the schools. The ratios Ca/Si, S/Si, S/Ca and (Si+Ca)/S have been established. Results obtained may be useful in epidemiological studies in the ceramic cluster area in order to estimate children’s exposure to different indoor primary school microenvironments. Effective policies and mitigation measurements for the protection of children’s health should be carried out in this highly industrialized area.

Morphological and micro-tomographic study on evolution of struvite in synthetic urine infected with bacteria and investigation of its pathological biomineralization.

Pathological biomineralization in the urinary system leads to urolithiasis. Formation of kidney stones involves a series of events during which they undergo morphological and mineralogical changes. We investigated the mineralization of biogenic struvite (in vitro) and examined the transformation of distinct interior and exterior structure of struvite. In vitro crystallization of struvite was performed in the presence of two bacteria that were originally isolated from the kidney stone patients. Morphological evaluation was carried out using SR-μCT as well as FESEM, XRD and FT-IR. Characteristic internal 3-D morphology and porosity of the stones were studied. For comparison, patient derived struvite stones were used. From the results obtained, we report that the presence of bacteria enhances the crystallization process of struvite in vitro. A series of time-resolved experiments revealed that struvite crystals experienced a significant morphologic evolution from pin pointed structure to X-shaped and tabular morphologies. These X-shaped and unusual tabular habits of struvite resembled biogenic morphologies of struvite. SR-μCT showed similarities between the patient derived and the in vitro derived struvite crystals. In conclusion, these experiments revealed that the bacteria play a major role in the specific morphogenesis of struvite and can able to control the nucleation, modulate crystalline phases, and shape of the growing crystal.

Calcite production by the calcifying green alga Phacotus lenticularis

The importance of carbonate precipitation by phytoplankton in fresh water lakes has not been sufficiently considered in global carbon cycles and climate change scenarios. The objective of this study was to determine the influence of the calcifying bivalved phytoflagellate Phacotus lenticularis (Ehrenberg) Deising 1866 on the total calcite precipitation in five European hard-water lakes. For this purpose, an accurate mass determination of single Phacotus lenticularis shells was required. We developed a novel methodological approach to precisely determine the volume and mass of the calcified shells. Focused ion beam (FIB) techniques were employed to investigate internal structural features. Thin layer cross-sections of the shell profiles were reproduced and perforation as well as the crystalline structure of the calcite plates were monitored. 3D-shell models were computed by 360° rotation of the shell cross-sections using a CAD 3D imaging software to calculate precise volumes and estimate realistic masses. In contrast to previous estimates, we determined a 2.8-fold higher shell mass of 0.86 ng CaCO3 (standard deviation SD = 0.18) for the highly massive shells at a mean volume per individual of 334.1 µm³ (SD = 70). An initial shell porosity of less than 5% was derived from thin layer cross-section images, resulting in a presumed mean shell density of 0.0026 ng µm−3. The shell diameter was significantly influenced by the lake’s origin. The shells from each lake displayed substantial variations in diameter and shape. The pores in the shells showed two variations. Wider pore canals penetrated the whole shell wall, whereas small, elongated pores were located along the interspaces between calcite crystals with tabular habit. The approximate average dimensions of these calcite plates were 1.0 × 1.6 × 0.2 µm. The mean lateral wall thickness at the rim and centre of the shell were 1.98 µm (SD = 0.42) and 0.79 µm (SD = 0.17), respectively. The average carbonate precipitation by Phacotus lenticularis in relation to the total epilimnetic suspended calcite precipitation was 6.0% in the oligotrophic lake Großer Ostersee (Bavaria, Germany). During the growing season, Phacotus lenticularis contributed up to 21% of the particulate calcium carbonate in the epilimnion. These findings suggest that Phacotus lenticularis should be considered in the assessment of hard-water lake carbon cycling.

Crystal growth, structural, spectral, thermal, linear and nonlinear optical characterization of a new organic nonlinear chiral compound: l-tryptophan-fumaric acid-water (1/1/1) suitable for laser frequency conversion

A new organic active nonlinear optical crystal l-tryptophan fumaric acid water (1/1/1), (C15H17N2 O7. H2O)(LTFAW), consisting of zwitterion tryptophan molecule in conjunction with a fumaric acid molecule and a water molecule was grown by slow solvent evaporation technique from aqueous solution. The organic chromophore crystallizes from water in its zwitterions exhibiting tabular habit in monoclinic system with acentric space group C2 (Z = 4). The sharp peaks observed in Powder X-ray diffractogram depicts the crystalline nature. The presence of functional groups in the grown crystal was analyzed using FT-IR spectrum. The carbon and hydrogen environment in molecular structure was investigated using FT-NMR technique using deuterated DMSO solution. Ultraviolet–visible spectral analysis reveal that the crystal possess lower cut-off wavelength down to 275 nm, is a key factor to exhibit Second Harmonic Generation (SHG) signal. The direct optical band gap is evaluated to be 5.28 eV from the UV absorption profile. The evaluation of optical constants by employing UV–visible absorbance data such as, extinction coefficient, reflectance, refractive index, optical conductivity are supportive towards good performance as NLO devices. Temperature of decomposition was investigated using thermogravimetric analysis/differential thermal analysis techniques (TG/DTA). The luminescence profile exhibited two peaks (362 nm, 683 nm) due to the donation of protons from carboxylic group to amino group. The nonlinear optical behavior from the noncentrosymmetric crystal was observed by the generation of frequency doubled (2ω) optical radiation when subjected to pulsed Nd:YAG laser (1064 nm, 10 ns, 10 Hz) using Kurtz-Perry method. The variation of dielectric constant (εʹ) and dielectric loss (εʹʹ) vs. Log f for the title compound was analysed at a few selected temperatures and frequencies.

GREENWOODITE, A NEW NESOSILICATE FROM BRITISH COLUMBIA WITH A Ba-VOH COUPLED SUBSTITUTION AND TETRAHEDRAL Fe: DESCRIPTION AND STRUCTURE

Greenwoodite, ideal formula Ba 2− x (V 3+ OH) x V 9 (Fe 3+ ,Fe 2+ ) 2 Si 2 O 22 , space group P 3m1, a 5.750(1) A, c 14.459(1) A, V 414.00(8) A 3 , Z = 1, is a new mineral from the Wigwam deposit of Southeastern British Columbia, Canada. It is a metamorphic mineral formed under greenschist-facies conditions as part of an assemblage that includes quartz, celsian, apatite, sphalerite, pyrrhotite, galena, pyrite, zoltaiite, and batisivite. Greenwoodite has a Mohs hardness of 5, one perfect cleavage, a semi-prismatic to tabular habit, and a calculated density of 4.81 g/cm 3 . It is opaque with reflectance and color similar to those of sphalerite. The strongest eight lines of the calculated X-ray powder diffraction pattern [ d in A ( I ) ( h k l )] are 2.925(100)(0 1 4), 2.875(38)(1 1 0), 2.672(23)(1 1 2), 2.469(35)(1 1 3), 2.354(28)(2 0 2), 2.212(28)(2 0 3), 1.669(26)(1 2 4), and 1.438(35)(2 2 0). The empirical formula, derived from microprobe analysis and the crystal structure, is Ba 0.60 (V 3+ OH) 0.40 (V 3+ 8.33 ,Cr 0.33 ,Ti 0.13 ,Al 0.13 ,Mn 3+ 0.02 ) ∑9 (Fe 3+ 1.08 ,Fe 2+ 0.60 ,Zn 0.22 ,Al 0.06 ,Mg 0.04 ) ∑2 (Si 1.72 ,Fe 3+ 0.28 ) ∑2 O 22 . The crystal structure was solved using direct methods for the location of Ba, V, and Fe and using Patterson synthesis and Fourier maps for the positions of the Si and O. The final R factor was 1.9% using 475 unique observed reflections. The structure is based on hexagonal closest packing (hcp) of oxygen atoms with 4 distinct cation layers designated BV, V1, V2, and V3 having a stacking sequence BV-V1-V2-V3-V2-V1-BV-V1- . . . The core layers (all layers except BV) contain 3 distinct V-dominated sites, one tetrahedral Si site and one Fe-dominated tetrahedral site containing a disordered mixture of equal amounts of trivalent and divalent cations. The BV layer is a disordered mixture of 2 endmember layer structures related by the coupled substitution 2Ba 2+ = 2O 2− + 2V 3+ + 1□ + 2H + . In the Ba endmember the Ba is at a cubo-octahedral site formed by a hole in one of the hcp oxygen layers. In the VOH endmember the Ba is replaced by an O atom which forms the shared corner of a triplet of octahedral sites. Only 2/3 of these sites are occupied, predominantly by V. Charge balance is achieved by bonding H to this O atom. The composition of the type grain of greenwoodite is 60% toward the Ba endmember of this coupled-substitution solid solution.

Geochemical and morphological characteristics of coarse-grained tabular beryl from the Xuebaoding W–Sn–Be deposit, Sichuan Province, western China

The dominant crystal faces on beryl are usually hexagonal prisms, a direct reflection of the lattice structure. However, coarse-grained beryl from the Xuebaoding W–Sn–Be deposit, China, has a tabular habit. To evaluate the genesis of this well-crystallized tabular beryl, we analysed the crystals using inductively coupled plasma mass spectrometry (ICP–MS), X-ray fluorescence (XRF) spectrometry, X-ray powder diffraction (XRD), and differential interference contrast microscopy (DICM). The beryl unit cell dimensions are 9.223–9.232 Å for a 0 and 9.183–9.244 Å for c 0. The ratio c 0 /a 0 = 0.995–1.002. The beryl has a high alkali content, including Li2O (2.60–3.10 wt.%), Rb (65–120 ppm), Cs2O (0.70–0.92 wt.%), and Na2O (1.29–1.66 wt.%); other components include TiO2 (0.00–0.01 wt.%), TFe2O3 (1.03–1.29 wt.%), MnO (0.01 wt.%), MgO (0.09–0.12 wt.%), and CaO (0.03–0.04 wt.%). These analyses indicate that the Xuebaoding material is a Na–Li–Cs beryl with a dominance of tetrahedral substitution in the crystal structure. Based on a systematic statistical study of the relationship between chemical composition and habit, a high content of alkalis leads to a lower growth rate of c {0001} compared with m , producing the short prismatic/columnar habit that typifies the Xuebaoding beryl. The difference in the number of pyramidal growth hillocks on s faces that face in opposing directions strongly suggests the influence of unidirectional hydrothermal fluid flow on growth rates. The oriented flow also led to variable growth rates for other crystal faces, including m and c {0001}, and caused the growth of many thick, distorted crystals of scheelite, cassiterite, tabular apatite, etc. Apparently, the m faces were outgrown by other, more rapidly growing faces and consequently tended to disappear. Accordingly, we discuss two mechanisms that underlie the formation of tabular beryl crystals: (1) the geochemical compositions and especially the high amount of alkalis at the Be site and in the channel structures of the crystals; and (2) the directional flow and supply of hydrothermal fluids in narrow fractures during crystal growth.

Crystallographic features of the primary Al 3Zr phase in as-cast Al-1.36 wt% Zr alloy

The habit and morphology of the primary Al 3Zr crystals formed during the solidification of Al-1.36 wt% Zr alloy were analyzed. It was observed that the crystals have a tabular habit. The longitudinal cuts of the smaller and larger sized crystals appear, respectively, in octagonal and rectangular forms. The primary crystals also appear in the dendritic form. A crystallographic study indicates that the smaller sized crystals are bound by {0 0 1}, {1 0 1} and {1 1 1} faceted planes, whereas the larger sized ones by {0 0 1} and {1 0 1} faceted planes. One compound twin with two variants is found in the dendritic crystals and the complete twinning elements are determined. The tabular habit of the primary crystals is attributed to the low roughness of {0 0 1} planes. The disappearance of {1 1 1} planes in the larger sized crystals result from their high roughness. The twin formation is realized by lattice shear plus local atom stacking fault accompanied by local atomic reshuffling. The dendritic crystals are the result of the formation of the compound twin.

ChemInform Abstract: Characterization of AlPO4-14 by Magic-Angle-Spinning Nuclear Magnetic Resonance Spectroscopy and Thermoanalytical and Adsorption Measurements.

AlPO4-14 has been prepared using piperidine as templating agent. Uniform crystals of tabular habit were obtained. By thermoanalytical measurements of the as-synthesized sample the content of occluded piperidine was determined and its degradation was followed. From the 31P MAS NMR spectra it follows that there should exist at least three non-equivalent sites in the framework of calcined AlPO4-14. Completely reversible changes in the 27Al and 31P MAS NMR spectra were found in dehydration/hydration cycles. The relative small pore diameter of AlPO4-14 (ca. 0.4 nm) prohibits the adsorption of n-alkanes. From the adsorption isotherms of methanol and water the saturation capacities were determined to be 0.17 and 0.27 cm3 g–1, respectively.

The crystal structure and hydrogen bonding of synthetic konyaite, Na2Mg(SO4)2{middle dot}5H2O

The crystal structure of synthetic konyaite, Na2Mg(SO4)2·5H2O, a = 5.7690(8), b = 23.951(3), c = 8.0460(11) Å, β = 95.425(2)°, V = 1106.8(3) Å3, space group P21/c, Z = 4, was solved using singlecrystal X-ray diffraction. Hydrogen atom positions were determined and the structure solution was refined to R1 = 3.31% and wR2 = 6.28% for the 2167 measured independent reflections. Three distinct cation sites host the Mg and Na atoms in distorted octahedra and eight-coordinated polyhedra. The coordination polyhedra share edges to form compact sheets oriented perpendicular to b and linked to one another by hydrogen bonds. This results in a {010} tabular habit. A comparison of this structure is made to that of blödite [Na2Mg(SO4)2·4H2O], the dehydration product of konyaite. Konyaite is discussed within the context of the Na2O-MgO-SO4-H2O system. This study is part of ongoing investigations into the dehydration mechanisms and phase stability of this system.

The crystal structure of piergorite-(Ce), Ca8Ce2(Al0.5 Fe0.53+) 1( ,Li,Be)2Si6B8O36(OH,F)2: A new borosilicate from Vetralla, Italy, with a modified hellandite-type chain

Piergorite-(Ce) is a new mineral found at Tre Croci, Vetralla, Italy with simplified formula Ca 8 Ce 2 (Al 0.5 Fe 0.5 3+ ) ∑1 (□,Li,Be) 2 Si 6 B 8 O 36 (OH,F) 2 . It occurs as strong intergrowths of small crystals, colorless to pale yellow, associated with sanidine, mica, magnetite, rutile, titanite, and other Th-U-REE bearing minerals, in miarolitic cavities of a syenitic ejectum. Piergorite-(Ce) is biaxial negative, n α = 1.717 (1), n β = 1.728 (1), and n γ = 1.735 (1), 2 V meas = 68(2)°, X = b , and Z ^ c = 7(1)°. Crystals show tabular habit and a very good {010} cleavage; twinning along the (301) plane produces “L” forms. The three strongest lines in the simulated powder diffraction pattern ( d obs , I , hkl ) are: 2.65 A, 100.0, (213, 413); 1.91 A, 48.3, (223, 423, 821); 2.90 A, 44.9, (603, 612). The structure was solved by Patterson synthesis from X-ray diffraction data [monoclinic, space group P 2/ a , a = 28.097(3) A, b = 4.777(1) A, c = 10.236(2) A, β = 96.81(1)°, V = 1364.2(7) A 3 , Z = 2] and was refined to a final R obs = 0.059 for 6480 F o with I o > 3σ ( I o ). The structure shows similarities with the hellandite group because Si and B tetrahedra form chains along c . Hellandite structure is characterized by a single chain of five-membered rings, whereas piergorite-(Ce) shows a double chain of five-membered rings interconnected by a single octahedral site to form a three-dimensional framework containing five independent eightfold-coordinated M sites and a partly occupied T-cavity.

Relationships between crystal morphology and composition in the (Ba,Sr)SO 4–H 2O solid solution–aqueous solution system

This paper deals with the relationship between habit and compositional changes in crystals of the Ba x Sr 1 − x SO 4 solid solution at 25 °C and 1 atm. Crystals corresponding to the whole range of compositions of the Ba x Sr 1 − x SO 4 solid solution have been grown in a diffusing–reacting system. The physicochemical evolution resulting from counter-diffusion of SrCl 2/BaCl 2 and Na 2SO 4 reactants along a silica hydrogel column results in the development of spatio-temporal crystallization sequences. The external habit and the internal zoning reflecting both the morphological and compositional evolution of the crystals have been studied by scanning electron microscopy, EDAX and microprobe analysis. As composition varies from barite to celestite end-members, a clear evolution both in internal crystal morphologies and in final habit of crystals grown along the gel column has been observed. The main change observed is in the relative development of {001} and {011} forms, which is accompanied by a change in the crystals elongation. While tabular habits dominated by the {001} pinacoid correspond to crystal compositions close to pure barite, crystals with compositions closer to celestite show elongated morphologies dominated by the {011} rhombic prism. This variation is also evident in the internal morphologies of the crystals. The progressive predominance of {011} forms as crystals become richer in Sr has been interpreted on the basis of surface structure description by Hartman–Perdok theory. Moreover, Atomic Force Microscopy investigations of the epitaxial growth of pure celestite on barite (001) surfaces under different degrees of supersaturation with respect to celestite have provided complementary quantitative information. Growth morphologies for different supersaturations with respect to celestite can be predicted using growth rates of crystal faces measured on a molecular scale. The results clearly show the effect of Sr incorporation into barite structure on the Ba x Sr 1 − x SO 4 crystal habit at a molecular scale. The results presented in this paper can help to develop morphological criteria relating morphology and composition of Ba x Sr 1 − x SO 4 crystals occurring in natural environments as a result of inorganic crystallization and biomineralization processes.

Leogangite, Cu 10 (AsO 4 ) 4 (SO 4 )(OH) 6 ???8H 2 O, a new mineral from the Leogang mining district, Salzburg province, Austria

Leogangite, ideally Cu10(AsO4)4(SO4)(OH)6·8H2O, was found on sample material from mine dumps of the Danielstollen and Inschlagalm in the Schwarzleo valley, both part of the polymetallic ore district of Leogang, Salzburg province, Austria. It is intergrown with olivenite and malachite, all together coating small voids within a tennantite-bearing dolomite breccia, and is assumed to have formed as an alteration product of arsenic-rich fahlore. Associated minerals are tyrolite, parnauite, strashimirite, euchroite, brochantite, langite, posnjakite, and devilline. The new mineral crystallizes with monoclinic symmetry, space group C2/c (no. 15), with a=21.770(7) A, b=12.327(4) A, c=10.720(3) A, β=92.85(1)°, V=2873(2) A3, Z=4, and a calculated density of 3.55 g·cm−3. Leogangite exhibits a thin tabular habit with aggregates of platelets flattened on {100} and elongated along [010], measuring up to 0.1 mm in length, 0.05 mm in width, 0.01 mm in thickness. A perfect cleavage parallel to (100) can be observed. It is transparent, green with a bluish tint, the streak is light green, and it is optically negative with 2V=18(2)°. The refractive indices nx, ny, and nz are 1.590(2), 1.740(2), and 1.744(2), the optical orientation is X=a*, Y=b, Z=c, and the pleochroism is blue-green (X) to pale green (Y, Z). Typical microprobe analyses give (wt%) CuO 49.6–52.9, As2O5 28.5–31.1, SO3 4.9–5.4, which is equivalent to Cu9.94(As0.99Si0.01O4)4(S0.99O4)(OH)6·8.89H2O as the average composition based on 20+3 oxygens. The strongest reflections of the X-ray powder diffraction pattern are (dobs, I/Iobs, hkl): 10.85, 100, (200); 2.630, 60, (\({\it 20}{\bar {\it 4}}\)); 5.44, 50, (400); 3.625, 50, (600); 3.090, 40, (023). The structure of the mineral was refined to R1=0.095 for 1768 unique reflections with \(F^2_{\rm o} > 4\sigma(F^2_{\rm o})\) and is a new representative of the rare [5]-coordinated Cu2+ compounds with edge-sharing CuO5 square pyramids. The main motif consists of [Cu4O14] tetramers. Together with the AsO4 tetrahedra and the remaining CuO5 polyhedron they build complex heteropolyhedral layers parallel to (100), which are linked by the SO4 tetrahedron and parts of the hydrogen bonds along the a-axis, thus forming a complex open framework structure. Chemical, optical and X-ray powder pattern characteristics are the distinguishing features to similar minerals like parnauite, tyrolite, or clinotyrolite.

Zircon typology, geochronology and whole rock Sr?Nd isotope systematics of the Mecsek Mountain granitoids in the Tisia Terrane (Hungary)

Zircon typology and ages together with petrological data suggest similarities in the origin of the K–Mg-rich granitoids of the Mecsek Mountains (Moragy Unit, Tisia Terrane, S Hungary) and the durbachitic to K–Mg-rich rocks of the South and Central Bohemian Batholiths. Our investigations evidence a characteristic bimodal distribution of zircon types and ages. Zircons of “normal” magmatic habit and a typology around S24 show an age of 354±5 Ma. Zircons of tabular habit of subtype S4 indicate a possibly younger age of 339±10 Ma. The ages and typology of zircons from plutonic rocks in the Mecsek Mountains strongly resemble those from the Rastenberg granodiorite in the South Bohemian Batholith (Austria). This, as well as Rb/Sr and Sm/Nd isotope systematics, support the assumption of simultaneous formation and close spatial relationship between the Mecsek Mountain granitoids and the Rastenberg granodiorite. Thus, the Mecsek Mountains granitoids likely formed in a Late Palaeozoic palaeo-position S or SSW of the Rastenberg granodiorite. Having experienced a similar metamorphic and magmatic evolution during the Carboniferous, at least the northernmost part of the Tisia Terrane, the Moragy Unit, is therefore considered to represent a former part of the Helvetic-Moldanubian zone.

WAGNERITE-Ma5bc, A NEW POLYTYPE OF Mg2(PO4)(F,OH), FROM GRANULITE-FACIES PARAGNEISS, LARSEMANN HILLS, PRYDZ BAY, EAST ANTARCTICA

Wagnerite- Ma 5 bc , a new polytype, occurs in paragneiss associated with banded cordierite–prismatine gneiss in the Larsemann Hills, East Antarctica. It forms anhedral to euhedral grains mostly 0.5–2 mm across, some with a tabular habit. Textures are consistent with a primary assemblage wagnerite- Ma 5 bc + plagioclase + apatite + magnetite + ilmenite–hematite that crystallized under granulite-facies conditions (750 – ~860°C, 6–7 kbar). Also present are biotite, quartz, K-feldspar, minerals of the monazite and xenotime groups, corundum, hercynite, and sulfide. Electron-microprobe analyses give P 2 O 5 41.39, SiO 2 0.06, TiO 2 0.88, FeO 4.16, MnO 0.09, MgO 44.54, CaO 0.09, F 6.87, H 2 O (calculated for OH + F = 1) 2.04, O=F −2.89, total 97.22 wt%, corresponding to (Mg 1.88 Fe 0.10 Ti 0.02 )(P 0.99 O 4 )(F 0.61 OH 0.39 ). The space group is Ia . Lattice parameters: a 9.645(2), b 31.659(6), c 11.914(2) A, β 108.26(3)°, V 3455(1) A 3 for Z = 40. The crystal structure has been solved by direct methods and refined to R 1 = 0.0413 for the independent 4521 reflections [I > 2σ(I)] using Mo K α radiation. The primary difference between the wagnerite- Ma 5 bc and wagnerite- Ma 2 bc ( e.g ., type locality) is ordering of the (F,OH) positions. F can occupy one of two positions, resulting in two distinct configurations along the a direction. In magniotriplite, the sequence of configurations in the b direction is disordered, whereas in wagnerite- Ma 2 bc , the sequence is ordered 121212… and in wagnerite- Ma 5 bc , 12112... Magniotriplite and the wagnerite polytypes do not overlap in composition: minerals richer in Fe and Mn (average ionic radius ≥ 0.76 A) crystallize as the disordered minerals in the triplite group, whereas highly magnesian minerals (average ionic radius ≤ 0.73 A or ≥ 86% of the Mg end member) crystallize as the ordered polytypes of wagnerite. Magniotriplite formed at moderate temperatures ( e.g., amphibolite-facies conditions), whereas wagnerite- Ma 2 bc is found in rocks formed under a wide range of P–T conditions. Compositional or kinetic factors (or both), rather than P–T , could play the leading role in determining the extent of F order; possibly many M 2+ 2 PO 4 F compounds originally crystallize in the disordered state, the Mabc polytype, and only magnesian varieties subsequently order on cooling, i.e ., Mn 2+ and Fe 2+ inhibit ordering.

Morphology of New (P2 1 /n) Metastable Anthracene Modification Crystals, Grown from the Vapor Phase

The morphology of the vapor-grown crystals of a new metastable anthracene modification (that crystallizes in the monoclinic space group P2 1 /n with a =8.553(2), b =6.021(1), c =22.334(4) Å, β=124.54(3)°, and four molecules per unit cell) was determined from the X-ray single crystal orientation data and optical reflection goniometry measurements. In the standard space group P2 1 /c, the crystals of this new phase possessed a rhomboidal tabular habit with two major {002} faces oriented in [001] direction, and twelve lateral faces of {11 \\bar{3} }, {111}, {100}, and {102}. This morphology differs nearly fully from that observed for the crystals of a long-known parent anthracene phase (P2 1 /a) grown under the same conditions. The experimental morphologies of both crystal phases were compared with those predicted from the periodic band chain (PBC) theory of Hartman and Perdok. Moreover, the melting point for this new metastable anthracene phase, equal to 215.1°C, was determined with help of a differential scanning calorimeter.

BIGCREEKITE: A NEW BARIUM SILICATE MINERAL SPECIES FROM FRESNO COUNTY, CALIFORNIA

The sanbornite deposits at Big Creek and Rush Creek, Fresno County, California, are host to many rare barium silicates. Bigcreekite, ideally BaSi2O5·4H2O, is a newly identified mineral species that occurs along very thin transverse fractures in laminated quartz-rich sanbornite portions of the rock. It postdates the other associated barium silicates and represents either a later primary phase from infiltrated fluids or a product of alteration of pre-existing Ba-rich minerals, possibly sanbornite. It is white to colorless and forms poorly developed crystalline masses parallel to the fracture direction. There are two perfect cleavages, {010} and {001}. Other physical properties are: tabular habit, elongate [100], brittle, non-fluorescent, vitreous to pearly luster, white streak, H 2–3, uneven fracture. Bigcreekite is biaxial positive, α 1.537(2), β 1.538(2), γ 1.541(2); X = b , Y = a , Z = c , 2 V meas 59.2(5)°, 2 V calc 60°; dispersion is moderate, r < v , and it is non-pleochroic. It is orthorhombic, space group Pnma , with unit-cell parameters refined from powder data: a 5.038(6), b 9.024(3), c 18.321(6) A, V 833(1) A3, Z = 4. The strongest six lines of the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 5.068(100)(013), 4.054(85)(022), 2.974(45)(031), 2.706(60)(124), 2.327(40)(035) and 2.257(75)(126). The empirical formula of bigcreekite (based on O = 9) is (Ba1.00Na0.01)∑1.01Si2.00H8.00O9.00. D calc = 2.76 g/cm3, and D meas = 2.66(3) g/cm3. The structure has been refined to R = 3.5%. Bigcreekite is a hydrous inosilicate; the SiO4 tetrahedra are arranged in four-membered rings that form chains parallel to [100] and are staggered in the [001] direction. Molecules of H2O fill the large spaces between the rows of silicate tetrahedra. The structure of bigcreekite has similarities to those of both sanbornite and gillespite. Bigcreekite was named after Big Creek, California, the type locality.