Rhombohedral Faces Research Articles

Quartz: An Unnamed Habit with Two Prominent Rhombohedral Faces

Quartz: An Unnamed Habit with Two Prominent Rhombohedral Faces

Zn2+-Pb2+-doped calcite shrub fabrics: Abiotic morphogenesis of travertine-like dripstone encrustation at the Jersey Zinc Mine, southeastern British Columbia

A cm-thick calcite dripstone on the floor of the abandoned Jersey Zinc Mine in southeastern British Columbia, western Canada, consists of a mixture of shrub and radial fibrous elongated columnar crystal fabrics that resulted from Zn2+ and Pb2+ doping of the calcite crystallographic lattice structure. These heavy metal elements were sourced from sulfide mineralized veins in the overlying limestone beds. Zn2+ and Pb2+ substitution for Ca2+ reduced the size of the calcite crystal structure, impacting configuration of the calcite crystal fabrics. Lower concentration levels of dopants resulted in a radial fibrous elongated columnar crystal fabric with high inter-crystalline porosity. Increased levels of Zn2+ and Pb2+ dopants resulted in a crystal splitting process forming the shrub fabric. Growth of normally flat rhombohedral face on the external surface of the dripstone encrustation was disrupted by mixtures of isotropic and anisotropic growth rates. Inhibited growth rates resulted in early stage crystal splitting processes, forming parallel arrays of precursor crystallites aligned as step-down micro-terraces separated by dam-like micro-barrage partitions with normal growth rates. Shrub fabrics developed below the encrustation surface as ion-laden dripwater films infiltrated the 20% to 25% inter-crystalline porosity. This early stage of crystal splitting transitioned into a shrub fabric substrate, each consisting of fan-shaped crystal arrays distributed along a main stem, all in optical continuity. Extreme levels of Zn2+ dopant resulted in split crystal formation of micro-spherulites on the external surface of the dripstone. Spherulite neomorphism occurred, resulting in replacement of the crystallites by an individual calcite spar during envelopment by the columnar crystal domain fabric. The spheroid forms were preserved within the columnar fabric as spheroid zones of Zn-calcite and outlined by microcrystalline ferroan calcite. The shrub fabrics have morphological similarity to dendritic branching shrubs commonly associated with biotic and abiotic travertine and some biotic tufa deposits, which form under very different depositional conditions. Abiotic Zn2+-Pb2+ dopants absorbed into the calcite crystal structure of this mine floor encrustation precluded the necessity for carbonate precipitation from supersaturated carbonate water or precursor microbial induced nucleation sites, unlike similar travertine and tufa shrub fabrics elsewhere.

Significance of Fracture-Filling Rose-Like Calcite Crystal Clusters in the SE Pyrenees

Fracture-filling rose-like clusters of bladed calcite crystals are found in the northern sector of the Cadí thrust sheet (SE Pyrenees). This unusual calcite crystal morphology has been characterized by using optical and electron microscope, X-ray diffraction, Raman spectroscopy, δ18O, δ13C, 87Sr/86Sr, clumped isotopes, and major and rare earth elements + yttrium (REEs + Y) analysis. Petrographic observations and powder X-ray diffraction measurements indicate that these bladed crystals are mainly made of massive rhombic crystals with the conventional (104) faces, as well as of possibly younger, less abundant, and smaller laminar crystals displaying (108) and/or ( 1 ¯ 08) rhombic faces. Raman analysis of liquid fluid inclusions indicates the presence of aromatic hydrocarbons and occasionally alkanes. Clumped isotopes thermometry reflects that bladed calcite precipitated from meteoric fluids at ~60–65 °C. The 87Sr/86Sr ratios and major elements and REEs content of calcite indicate that these fluids interacted with Eocene marine carbonates. The presence of younger ‘nailhead’ calcite indicates later migration of shallow fresh groundwater. The results reveal that rose-like calcite clusters precipitated, at least in the studied area, due to a CO2 release by boiling of meteoric waters that mixed with benzene and aromatic hydrocarbons. This mixing decreased the boiling temperature at ~60–65 °C. The results also suggest that the high Sr content in calcite, and probably the presence of proteins within hydrocarbons trapped in fluid inclusions, controlled the precipitation of bladed crystals with (104) rhombohedral faces.

The sense of balance in humans: Structural features of otoconia and their response to linear acceleration.

We explored the functional role of individual otoconia within the otolith system of mammalians responsible for the detection of linear accelerations and head tilts in relation to the gravity vector. Details of the inner structure and the shape of intact human and artificial otoconia were studied using environmental scanning electron microscopy (ESEM), including decalcification by ethylenediaminetetraacetic acid (EDTA) to discriminate local calcium carbonate density. Considerable differences between the rhombohedral faces of human and artificial otoconia already indicate that the inner architecture of otoconia is not consistent with the point group -3m. This is clearly confirmed by decalcified otoconia specimen which are characterized by a non-centrosymmetric volume distribution of the compact 3+3 branches. This structural evidence for asymmetric mass distribution was further supported by light microscopy in combination with a high speed camera showing the movement of single otoconia specimen (artificial specimen) under gravitational influence within a viscous medium (artificial endolymph). Moreover, the response of otoconia to linear acceleration forces was investigated by particle dynamics simulations. Both, time-resolved microscopy and computer simulations of otoconia acceleration show that the dislocation of otoconia include significant rotational movement stemming from density asymmetry. Based on these findings, we suggest an otolith membrane expansion/stiffening mechanism for enhanced response to linear acceleration transmitted to the vestibular hair cells.

Growth history and textures of quartz twinned in accordance with the Japan law

The growth history of quartz twinned according to the Japan law and the development of fine textures near Japan twin boundaries were analysed using optical microscopy, cathodoluminescence, and computational simulations. Cathodoluminescence images of the samples show two distinct growth stages. In the early growth stage, growth sectors of rhombohedral faces bordered by the {1122} composition plane serve as preferential growth sites that grow approximately 1.5–1.8 times faster than the other symmetrically equivalent faces. Thus, the samples initially exhibit a “fan-shape”. The composition plane is quite straight and parallel to {1122} in the growth sectors of rhombohedral faces but undulates in the growth sectors of prism faces. In the later growth stage, the twinned crystals grow rather isotropically and change into “V-shape”. Prism faces start to develop at the composition plane, which is no longer parallel to {1122}. Observations of etched figures show that fine Brazil twin lamellae are concentrated almost exclusively near the Japan twin boundary. In the early growth stage, polysynthetic Brazil twin lamellae are formed in an hourglass-shaped sector, and the lamellae develop progressively as the Japan twin grows. However, there are considerably fewer lamellae in the later growth stage. Structures at the intersection of Japan and Brazil twin boundaries were modelled using molecular dynamics simulations. The intersections of Brazil and Japan twin boundaries were found to be structurally coherent when they have certain composition planes. The results imply that Japan twin boundaries only have structural diversity, allowing either right-handed or left-handed quartz to grow coherently on the substrate crystals, when the composition plane of Japan twin is parallel to {1122} and rhombohedral faces are bordered by the {1122} composition plane. This structural diversity of the {1122} Japan twin boundaries causes development of fine Brazil twin lamellae and triggers faster growth rate of rhombohedral faces bordered by the straight {1122} composition plane.

Crystalline organization of the fibrous prismatic calcitic layer of the Mediterranean mussel Mytilus galloprovincialis

The outer layer of the shell of members of the genus Mytilus is made of long, slender fibres of calcite (some 1–2 μm wide and hundreds of μm long), which reach the internal surface of the shell at an angle. This microstructure has been called anvil-type fibrous calcitic and its organization, crystallography and relationships to the organic phase are poorly known. We have studied the outer calcitic layer of the Mediterranean mussel M. galloprovincialis by means of optical and scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD) and atomic-force microscopy (AFM). SEM data from other species have also been gathered. All data together imply that the material is extremely well ordered both from the morphological and crystallographic viewpoints. The XRD pole figures show that there are discrete 001 and 104 maxima; therefore, the material has a well-defined sheet texture. In living animals there is an organic membrane (surface membrane) that coats the inner surface of the shell. TEM sections of the decalcified material show that this mainly proteinaceous surface layer is internally laminated and fills all the spaces left between the growing fibres. Every fibre is a monocrystal with three well developed {104} rhombohedral faces at its growth end. One of these faces is directly in contact with, and strictly parallel, to the sublayers of the surface membrane and thus to the inner shell surface. AFM experiments consisting on growing calcite onto shell pieces in which the surface membranes are preserved, show that the calcitic fibres of the shell easily regrow across the membrane, demonstrating that it is permeable to ions. In this way, prisms are able to grow despite the existence of the intermediate membrane in the living animal. Additional experiments of calcite growth onto the inner side of the surface membrane show that crystals grow onto their {104} surfaces. The surface membrane is responsible for the high degree of ordering of the fibrous calcitic layer, because it stabilizes the orientation of a rhombohedral surface, once this is parallel to the protein sublayers. This is one of the very few cases in which the influence of the organic matter on the organization of microstructures can be demonstrated.

Effects of crystal orientation on the dissolution of calcite by chemical and microscopic analysis

The purpose of this work was to examine the effects of polished crystal-surface orientation and degree of solution undersaturation on the dissolution kinetics of calcite. Crystallographic surface orientations utilized in this study included natural calcite specimens polished approximately parallel to the (104) plane, giving rise to surfaces with flat terraces with few steps, as well as fully kinked surfaces created by sectioning approximately parallel to the (001) plane. Results from inductively coupled plasma optical emission spectroscopy (ICP-OES) and vertical scanning interferometry (VSI) investigations revealed how crystallographic orientations of calcite with initially higher energy surface morphologies were associated with greater extent of reaction, greater surface retreat, and therefore, greater initial transient dissolution rates than those with lower energy initial surface morphologies. However, both the ICP-OES and atomic force microscopy (AFM) results confirm that the effects of crystal orientation become minimal under long-term conditions because (1) variously oriented calcite surfaces exhibited similar “long-term” rates and (2) orientations with high initial reactive site densities developed lower energy morphologies. Estimating a step rate coefficient from the experimental data from a miscut sample suggest that these coefficients may be highly morphology dependent. Results from this study are significant for predicting long term calcite dissolution rates because they suggest that the “long-term” dissolution rate of calcite will be governed by the rates of the rhombohedral faces and microfacets and the time-scale for approaching such conditions is of the order of days at room temperature and slightly alkaline solution conditions.

Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime

Phase and morphology evolution of CaCO3 precipitated during carbonation of lime pastes via the reaction Ca(OH)2 + CO2 → CaCO3 + H2O has been investigated under different conditions (pCO2 ≈ 10−3.5 atm at 60 % RH and 93 % RH; pCO2 = 1 atm at 93 % RH) using XRD, FTIR, TGA, and SEM. Simulations of the pore solution chemistry for different stages and conditions of carbonation were performed using the PHREEQC code to investigate the evolution of the chemistry of the system. Results indicate initial precipitation of amorphous calcium carbonate (ACC) which in turn transforms into scalenohedral calcite under excess Ca2+ ions. Because of their polar character, $$ \left\{ {21\bar{3}4} \right\} $$ scalenohedral faces (type S) interact more strongly with excess Ca2+ than non-polar $$ \left\{ {10\bar{1}4} \right\} $$ rhombohedral faces (type F), an effect that ultimately favors the stabilization of $$ \left\{ {21\bar{3}4} \right\} $$ faces. Following the full consumption of Ca2+ ions and further dissolution of CO2 leading to a pH drop of the pore solution, $$ \left\{ {21\bar{3}4} \right\} $$ scalenohedra are subjected to dissolution. This eventually results in re-precipitation of $$ \left\{ {10\bar{1}4} \right\} $$ rhombohedra at close-to-neutral pH. This crystallization sequence progresses through the carbonated depth with a strong dependence on the degree of exposure to CO2, which is controlled by the carbonated pore structure governing the diffusion of CO2. Both the carbonation process and the scalenohedral-to-rhombohedral transformation are kinetically favored under high RH and high pCO2. Supersaturation plays a critical role on the nucleation density and size of CaCO3 crystals. These results have important implications in understanding the behavior of ancient and modern lime mortars for applications in architectural heritage conservation.

Cossaite, (Mg0.5,☐)Al6(SO4)6(HSO4)F6·36H2O, a new mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy

AbstractCossaite, ideally (Mg0.5,☐)Al6(SO4)6(HSO4)F6·36H20, was found in the altered pyroclastic breccia of an active fumarole (T about 350°C) located at the rim of the La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. Cossaite is trigonal, space group R3̄, with a = 22.010(2), c = 9.238(1) Å, V = 3875.6(6) Å3, Z = 3. It forms stout prismatic hexagonal crystals up to 100 μm in size, terminated by rhombohedral faces, and is associated with thermessaite, vlodavetsite, sassolite and salammoniac. Cossaite is colourless to white, the streak is white and the lustre vitreous. It is not fluorescent in either long-wave or short-wave ultraviolet radiation. The calculated density is 2.075 g cm–3. The mean refractive index nobs is 1.49(1) (589 nm). Chemical analysis gave MgO 1.4, A12O3 19.5, SO3 34.7, F 5.7, (H2O 40.85, from structure refinement), O=F –2.4, total 99.75 wt.%, corresponding to the empirical formula Mg0.56Al6.19S7.01H73.37F4.85O65.15 calculated on the basis of 70 oxygen plus fluorine atoms. The strongest six lines in the X-ray powder diffraction pattern [dobs(Å) (I) (hkl)] are: 4.15 (100) (140), 3.87 (70) (32̄2), 11.00 (50) (110), 4.58 (25) (131), 2.770 (20) (3̄33), 2.166 (20) (1̄8̄1). The crystal structure was refined to a final R index of 0.0349. It contains octahedral [A1(H2O)5F]2+ cations and sulphate anions interacting via hydrogen bonds to form channels running along [001], where disordered [Mg(H2O)6]2+ cations and hydrogensulphate anions are hosted.

Structural Relationship between Calcite–Gelatine Composites and Biogenic (Human) Otoconia

AbstractBiogenic otoconia (ear dust) are composite materials of calcite with about 2 wt.‐% proteins showing an average longitudinal size of about 10 μm. The tiny biomineral particles are situated in the inner ear (in the maculae) and act as sensors for gravity and linear acceleration. Our comparative study of calcite–gelatine composites (grown by double diffusion) and human otoconia is based on decalcification experiments, scanning electron microscopy, TEM and X‐ray investigations in order to obtain a complete picture of the 3D structure and morphogenesis of the materials. Otoconia as calcite–protein composites display a cylindrical body with terminal rhombohedral faces intersecting at the pointed ends. As evidenced by TEM on focused ion beam cuts, both the artificial composites and human otoconia show a particular distribution of areas with different volume densities leading to a dumbbell‐shape of the more dense parts consisting of rhombohedral branches (with end faces) and a less ordered, less dense area (the belly region). The peculiar inner architecture of otoconia with its dumbbell‐shaped mass/density distribution is assumed to be necessary for optimal sensing of linear accelerations.

Lattice-preferred orientations of late-Variscan granitoids derived from neutron diffraction data: implications for magma emplacement mechanisms

The lattice-preferred orientation (LPOs) of two late-Variscan granitoids, the Meissen monzonite and the Podlesí dyke granite, were determined from high-resolution time-of-flight neutron diffraction patterns gained at the diffractometer SKAT in Dubna, Russia. The results demonstrate that the method is suitable for the LPO analysis of polyphase, relatively coarse-grained (0.1–6 mm) rocks. The Meissen monzonite has a prominent shape-preferred orientation (SPO) of the non-equidimensional minerals feldspar, mica and amphibole, whereas SPO of the Podlesí granite is unapparent at the hand-specimen scale. The neutron diffraction data revealed distinct LPOs in both granitoids. The LPO of the non-equidimensional minerals feldspar, mica and amphibole developed mainly during magmatic flow. In the case of the Meissen monzonite, the magmatic flow was superimposed by regional shear tectonics, which, however, had no significant effect on the LPOs. In both samples, quartz shows a weak but distinct LPO, which is atypical for plastic deformation and different in the syn-kinematic Meissen monzonite and the post-kinematic Podlesí granite. We suggest that, first of all, the quartz LPO of the Meissen monzonite is the result of oriented growth in an anisotropic stress field. The quartz LPO of the Podlesí granite, which more or less resembles a deformational LPO in the flattening field of the local strain field, developed during magmatic flow, whereby the rhombohedral faces of the quartz crystals adhered to the (010) faces of aligned albite and to the (001) faces of zinnwaldite. Due to shape anisotropy of their attachments, the quartz crystals were passively aligned by magmatic flow. Thus, magmatic flow and oriented crystal growth are the major LPO-forming processes in both granitoids. For the Meissen monzonite, the solid-state flow was too weak to cause significant crystallographic re-orientation of the minerals aligned by magmatic flow. Finally, the significance of our results for the evaluation of the regional tectonic environment during magma emplacement is discussed. The discussion on the regional implications of the more methodologically oriented results provides the basis for future, more regionally aimed studies in view of the fabric characteristics of such plutons and their developing mechanisms.

Facile synthesis of elongated calcite superstructure by triblock copolymers with precisely designed block length

Calcite crystals elongated along the c-axis and capped by (1 0 4) rhombohedral faces were grown in the solutions of two kinds of triblock copolymers poly (ethylene glycol)- block-poly (acrylic acid)- block-poly ( n-butyl acrylate) (PEG- b-PAA- b-P nBA) with different PAA block length. The copolymer with 3:1 PEG:PAA block ratio facilitates the formation of spindle-shaped calcite elongated along the c-axis and with curved (1 0 0) or (1 1 0) prismatic faces. CaCO 3 obtained from the copolymer with 6:1 PEG:PAA block ratio exhibits stack-like calcite elongated along the c-axis and with no newly developed faces. The formation of elongated calcite could be due to the aggregation of nanoparticles via an oriented attachment mechanism. The calcite crystals recovered their rhombohedral {1 0 4} faces gradually with decreasing PAA block length from 3:1 to 6:1 PEG:PAA block ratio, which could be attributed to the weakening of the inhibition efficiency of the PAA block on the non-rhombohedral planes.

Crystallography of the Calcitic Foliated-Like and Seminacre Microstructures of the Brachiopod Novocrania

Previous studies on the calcitic seminacre of the craniid brachiopod Novocrania have never fully resolved the crystallography of its constituent calcite crystals. With this aim, we studied the tablets forming the foliated-like and seminacre layers of this brachiopod by means of scanning electron microscopy coupled to electron backscatter diffraction. In both cases, tablets are monocrystalline and have a common crystallographic structure. Their c axes lie approximately parallel to the shell surface, and, for those tablets forming the internal shell ribs, they are also parallel to the rib elongation. There is no consistency in the orientation of the a axes in the different plates. Crystal competition processes appear to be responsible for this fiber texture. The tablets are bounded by planar rhombohedral faces. The main, innermost surface is not a crystal face but marks the boundary of the crystal with the mantle epithelium. Our data also show that, during spiral growth, the crystal axes of seminacre tablets remain stationary. Calcite twins occasionally develop in the species Novocrania anomala. The foliated-like and seminacre microstructures are crystallographically dissimilar to the foliated layer of molluscs but similar to the foliated layer of bryozoans. The relationship of brachiopod seminacre to the molluscan nacre is also discussed.

Evidence of growth and sector zoning in hydrothermal quartz from Alpine veins

Several quartz crystals from three different Alpine vein localities and of known petrologic setting and evolution have been examined for possible elemental sector zoning in order to help to constrain the mechanisms of such trace element incorporation. Using different in situ techniques (EMPA, LA-ICPMS, SIMS, FTIR-spectroscopy), it was established that Al and Li concentrations can exceed several hundreds of ppma for distinct growth zones within crystals formed at temperatures of about 300 °C or less and that also display patterns of cyclic growth when examined with cathodoluminescence. In contrast, crystals formed at temperatures closer to 400 °C and without visible cyclic growth have low concentrations of Al and Li as well as other trace elements. Al and Li contents are correlated along profiles measured within the crystals and in general their proportion does not change along the profiles. No relationships were found between Al, Na, and K, and germanium has a qualitative relationship with Al. FTIR spectra also show OH − absorption bands within the quartz, with higher amplitudes in zones rich in Al and Li. Sector zoning is present. It is most pronounced between prismatic and rhombohedral faces of the same growth zone, but also between the rhombohedral faces of r and z , which contain different amounts of trace elements. The sector zoning is also expressed by changes in the Li/Al ratio, with higher ratios in z compared to r faces. It is concluded that the incorporation of trace elements into hydrothermal quartz from Alpine veins is influenced by growth mechanisms and surface-structures of the growing quartz crystals, the influence of which may change as a function of temperature, pH, as well as the chemical composition of the fluid.

A scanning electron microscopic study to observe the changes in the growth morphology of the α phased Alumina–13 wt.% titania coatings during plasma spraying

Plasma spraying of Alumina–13 wt.% titania coatings shows preferential stability of α phase, in the as sprayed conditions, to an extent of 15–40%. As reported in the literature, the quantity of this α phase can be considered to be closely related to the processing parameters of the air plasma spray process, such as arc current, plasma gas flow rate etc. Normally, a lower value of arc current, results in larger quantity of preferentially stabilized α phase. In this paper, we have attempted to measure the orientation image mapping (OIM) of these α phased Alumina–13 wt.% titania coatings with Electron Back Scattered Diffraction. From the OIM, the pole figures for the α phase were established and from appropriate pole figures, such as (0001), (0006), (01 ī 1) and (10 ī 1) the growth morphology of the α phase could be determined. For larger values of arc current, at which the growth rate is faster and due to the imposed rapid solidification conditions, the hexagonal basal plane of (0001)-H type of the α phase tends to align with the (001) type FCC faces of the metastable γ phase. This alignment can be considered to be similar to a directionally solidified chill cast texture. On the other hand, at slower growth rate and at lower arc current value not only a larger quantity of α phase forms, but for accommodation of these larger number of α grains in the thinner section of splats there appears to be a need for a change in the growth morphology. (100)-R type rhombohedral faces, with shorter axial dimensions were found to align in preference to the directional solidified (0001)-H type basal planar arrangement. This type of change in growth morphology can possibly accommodate more α grains for the same thickness of the splat as compared to a basal plane (0001)-H type arrangement.

Crystallographic structure of the foliated calcite of bivalves

The foliated layer of bivalves is constituted by platy calcite crystals, or laths, surrounded by an organic layer, and which are arranged into sheets (folia). Therefore, the foliated microstructure can be considered the calcitic analogue to nacre. In this paper, the foliated microstructure has been studied in detail using electron and X-ray diffraction techniques, together with SEM observations on naturally decalcified shells, to investigate the crystallographic organization on different length scales and to resolve among previous contradictory results. This layer is highly organized and displays a coherent crystallographic orientation. The surface of the laths of the foliated layer is constituted by calcite crystals oriented with their c-axis tilted opposite to the growth direction of the laths and one of its { 1 0 1 ¯ 4 } rhombohedral faces looking in the growth direction. These faces are only expressed as the terminal faces of the laths, whereas the main surfaces of laths coincide with { 1 0 1 ¯ 8 } rhombohedral faces. This arrangement was consistently found in all specimens studied, which leads us to the provisional conclusion that, unlike previous studies, there is only one possible crystallographic arrangement for the foliated layer. Future studies on other species will help to ascertain this assertion.

Quartz aggregates revisited

Quartz aggregates that formed by coalescence of quartz crystals in the magma or in hydrothermal solution are considered. If the individuals have rhombohedral faces in contact, there will be two special cases: parallel intergrowths and intergrowths that agree in orientation and contact plane with Esterel twins grown from a twinned nucleus. For all other known cases, i.e. when the relative orientation satisfies the Japan, Sardinian, Tiflis, Zyndel-A or Samshvildo law, both individuals have exactly coinciding short symmetry translations in only one direction in the contact plane (monoperiodic twins). If a rhombohedral face is in contact with a prism face, monoperiodic twins will occur if the relative orientation satisfies the Zinnwald, Disentis or a proposed hypothetic law. The orientation of the two lattices can be expressed by a 180 degrees rotation about an axis with low indices independent of c/a in the case of the Esterel, Japan and Sardinian laws. The same is true for the Tiflis and Zyndel-A laws only if they are redefined, and not at all in the case of the Samshvildo, Zinnwald, Disentis and hypothetic laws. When the two individuals have rhombohedral faces in contact, there will even be exact two-dimensional coincidence (multiplicity sigma) in the contact plane and exact three-dimensional coincidence (multiplicity Sigma) in space if the square of the axial ratio c/a is rational. Indications are found that (despite their high values) these multiplicities may be related to the frequency of occurrence of intergrowths in low- and high-quartz.

Purification, Characterization, and in VitroMineralization Studies of a Novel Goose Eggshell Matrix Protein, Ansocalcin

Biomineralization is an important process in which hard tissues are generated through mineral deposition, often assisted by biomacromolecules. Eggshells, because of their rapid formation via mineralization, are chosen as a model for understanding the fundamentals of biomineralization. This report discusses purification and characterization of various proteins and peptides from goose eggshell matrix. A novel 15-kDa protein (ansocalcin) was extracted from the eggshell matrix, purified, and identified and its role in mineralization evaluated using in vitro crystal growth experiments. The complete amino acid sequence of ansocalcin showed high homology to ovocleidin-17, a chicken eggshell protein, and to C-type lectins from snake venom. The amino acid sequence of ansocalcin was characterized by the presence of acidic and basic amino acid multiplets. In vitro crystallization experiments showed that ansocalcin induced pits on the rhombohedral faces at lower concentrations (<50 microg/ml). At higher concentrations, the nucleation of calcite crystal aggregates was observed. Molecular weight determinations by size exclusion chromatography and sodium dodecyl sulfate -polyacrylamide gel electrophoresis showed reversible concentration-dependent aggregation of ansocalcin in solution. We propose that such aggregated structures may act as a template for the nucleation of calcite crystal aggregates. Similar aggregation of calcite crystals was also observed when crystallizations were performed in the presence of whole goose eggshell extract. These results show that ansocalcin plays a significant role in goose eggshell calcification.

CERITE-(La), (La,Ce,Ca)9(Fe,Ca,Mg)(SiO4)3[SiO3(OH)]4(OH)3, A NEW MINERAL SPECIES FROM THE KHIBINA ALKALINE MASSIF: OCCURRENCE AND CRYSTAL STRUCTURE

Cerite-(La), ideally (La,Ce,Ca) 9 (Fe,Ca,Mg)(SiO 4 ) 3 [SiO 3 (OH)] 4 (OH) 3 , was found in an aegirine – natrolite – microcline vein in foyaite, Mt. Yuksporr, Khibina massif, Kola Peninsula, Russia. It forms porous pseudomorphs (up to 7 cm long) after an unidentified hexagonal prismatic mineral. Within the pseudomorphs, cerite-(La) occurs as a boxwork-like aggregates of equant to tabular crystals (flattened on c , up to 2 mm across), with dominant rhombohedral and pinacoidal faces. Associated minerals are aegirine, anatase, ancylite-(Ce), barylite, catapleiite, cerite-(Ce), chabazite-Ca, edingtonite, fluorapatite, galena, ilmenite, microcline, natrolite, sphalerite, strontianite and vanadinite. The mineral is brittle, with a conchoidal fracture. It is light yellow to pinkish brown with a white streak, and translucent with a vitreous luster. Cleavage and parting were not observed. The Mohs hardness is 5; the density is 4.7(1) g cm −3 (meas.) and 4.74 g cm −3 (calc.). It is uniaxial, optically positive, n o 1.810(5), n e 1.820(5) (for λ = 589 nm). An average result of seven electron-microprobe analyses for seven different crystals (each one reported as an average of 6–10 points from each crystal) gave La 2 O 3 37.57, Ce 2 O 3 23.67, Pr 2 O 3 0.61, Nd 2 O 3 1.48, Sm 2 O 3 0.10, Gd 2 O 3 0.24, SrO 1.97, CaO 5.09, Fe 2 O 3 1.40, MgO 0.51, SiO 2 22.38, P 2 O 5 0.63, H 2 O 3.20 (determined by the Penfield method), total 98.85, which corresponds to the empirical formula (La 4.23 Ce 2.65 Ca 1.37 Sr 0.35 Nd 0.16 Pr 0.07 Gd 0.02 Sm 0.01 ) ∑8.86 (Fe 0.32 Ca 0.30 Mg 0.23 ) ∑0.85 [SiO 4 ] 3 [(Si 0.84 P 0.16 ) ∑1.00 O 3 (OH)] 4 (OH) 2.78 , calculated on the basis of (Si + P) = 7. The mineral is trigonal, R 3 c , with a 10.7493 (6), c 38.318 (3) A, V 3834.36 A 3 , Z = 6. The strongest eight lines in the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 3.53(26)(10.10,211), 3.47(40)(122), 3.31(38)(214), 3.10(25)(300), 2.958(100)(02.10), 2.833(37)(128), 2.689(34)(220), 1.949(34)(238,13.13). The crystal structure has been refined on the basis of F 2 for all unique reflections collected using a CCD area detector, to an R 1 of 0.036, calculated for the 1544 unique observed reflections ( F o ≥ 4σ F o ). Cerite-(La) is structurally related to cerite-(Ce). The mineral is named as the La-dominant analogue of cerite-(Ce). The structural formula for these minerals can be written as REE 9 M Ca x [SiO 4 ] 3 [SiO 3 ((OH) 1− x O x )] 3 [SiO 3 (OH)] 1− x (OH) 3 , where REE stands for La or Ce, and where M represents Fe, Mg, Ca.

Equilibrium form of negative crystals in igneous quartz.

Morphology and internal textures of negative crystals in igneous quartz were studied by combining microscopic observation and annealing experiments of natural specimens. Judged from its symmetry and the annealing experiments, the equilibrium form of the negative crystals is estimated to be rounded bipyramidal. The rounded bipyramidal shape suggests that only rhombohedral faces are singular under the growth conditions of quartz crystals in felsic magmas. Thermal history of these crystals after the eruption of magmas was estimated by the morphology and the internal texture of the negative crystals.