Platy Crystals Research Articles

Flux growth of LiNdP 4O 12 single crystals

LiNdP 4O 12 single crystals were grown by slow-cooling a Li 2OP 2O 5 flux. Crystal morphology and macroscopic crystal quality depend on the solution composition in the ternary system Li 2ONd 2O 3P 2O 5. Under the favorable growth conditions, platy crystals of 15 × 10 × 1 mm 3 were obtained.

An occurrence of polymorphic halloysite in granite saprolite of the Bayerischer Wald, Germany

AbstractXRD, DTA and IR patterns showed clay veins filling fissures in a granite of the Bayerischer Wald (eastern Bavaria) to consist mainly of hydrated halloysite of low crystallinity with traces of gibbsite, 2:1 (mixed layer) clay minerals and iron oxides. The halloysite forms thin plates which exhibit varying degrees and types of enrolment, resulting in platy, tubular and spheroidal crystals within the same sample. Concentrations of the trace elements Rb, Sr, Ba, Zr, Y, Ce, Pb, Zn and Cu indicate halloysite formation to have taken place via an aqueous phase under the influence of vadose waters circulating in fissures.

Lattice vibrations of boehmite (γ-AlOOH): Evidence for a C122 v rather than a D172 h space group

The lattice vibrations of boehmite can be separated into O 2− translations, lying between 500 and 765 cm −1 and OH − translations, lying between 300 and 410 cm −1. Comparison of the i.r. spectra of random and oriented preparations of platy crystals allows the recognition of transition moments perpendicular to the plates. Bands additional to those required by the statistical symmetry indicated by diffraction ( D 17 2 h , Cmcm) establish that the true space group must be C 12 2 v ( Cmc2 1), each domain of which probably extends over an entire hydrogen bonded double hydroxyl sheet.

Formation of 14Å Tobermorite from Silica Glass

14Å tobermorite was easily synthesized by using silica glass as a starting siliceous material. Silica glass (SiO2 99.97%, Blaine specific surface 1, 550cm2/g) was mixed with CaO at Ca/Si mol ratio of 0.7. The water/solid ratio was 20:1 by weight. The slurry was cured at 100°C for 2 to 7 days in an autoclave with stirring.The product was 14Å tobermorite of lath-like and platy crystals. The Ca/Si mol ratios were, 0.89 for 2 days reaction and 0.73 for 7 days reaction.Dehydration of the 14Å tobermorite gave 11Å tobermorite, but the 11Å tobermorite could not be converted to 9Å tobermorite on heating at higher temperatures. The 11Å tobermorite, therefore, belongs to an anomalous type. This kind of anomaly in the thermal behaviour has not yet been reported to be found among 14Å tobermorites.

A Spinifex Rock from Munro Township, Ontario

The textural and compositional characteristics of a spinifex rock (MS-1) from Munro township, Ontario have been investigated in some detail. When projected into Mg–CaO–Al2O3 and CaO–MgO–FeO space, MS-1 appears late in the fractionation trends for peridotites, associated spinifex rocks and high Mg basalts. The latter trend extrapolates almost linearly to olivine tholeiite compositions.There are two types of blade megacrysts in the rock, both apparently representing preexisting olivine: (1) an earlier phase of composite, skeletal platy crystals of clinochlore, about 10 × 10 × 0.5 mm in size, which have a preferred orientation in the rock and show pronounced parallel growth development in the plane of the blades. The clinochlore is crystallographically related to the host olivine with c* and [100] parallel to a and b axis of olivine, respectively; (2) sheafs of oriented skeletal plates about 0.1 mm in shortest dimension which are completely altered to chlorite, calcite, magnetite and amphibole. The appearance of the composite blade megacrysts varies markedly with thin section orientation and this seems to account for the various types of blade (or platey) crystals reported in the literature. The interblade areas are largely of acicular and spherulitic pyroxene and interstitial groundmass. The acicular pyroxene is augite. Its composition varies considerably, especially with the area analysed, the greatest variations being in Cr, Ti and Na. The augite is characterized by high Al contents—preferentially accommodated in tetrahedral sites—and this leads to a distinctive field in Ti, Al plots compared to those for lunar and other terrestrial pyroxene. The rock also contains a few relict rounded olivine phenocrysts, amygdules, accessory chromite octahedra with magnetite rims, pentlandite and pyrrhotite.The Mg–Fe ratios for the clinochlore, augite and interstitial groundmass do not vary greatly from that of the whole rock value in contrast to the situation in a quenched plateau basalt.

Origin and Distribution of Silica Lepispheres in Porcelanite from the Monterey Formation of California

ABSTRACT Samples of porcelanite from the Monterey Formation (Miocene) of California were examined by scanning electron microscopy and were found to contain numerous small cavities partially filled with platy crystals. The crystals, interpreted as opal-CT, occur as linings on cavity walls and as lepispheres (microspherical aggregates) within cavities. Based on the distribution and radial structure of the lepispheres and on previous experimental studies of synthetic lepispheres, it is suggested that the crystals precipitated from colloidal silica that was concentrated within cavities formed by localized solution of the lithified porcelanite groundmass. A colloidal origin is also suggested for lepispheres reported from deep sea sediments and for cherts that exhibit pervasive microspherical textur s.

Calcite Cementation of a Quaternary Conglomerate in Southern Sinai

ABSTRACT The lithic arenite groundmass of a polymictic conglomerate is cemented by two types of low magnesium calcite cement. Micrite, generally as polyhedral blocks and rarely as platy crystals, forms narrow rims around floating quartz grains and rock fragments. Sparite forms a drusy mosaic infilling between the micrite rimmed grains and fragments. Both forms of calcite are thought to be inorganic, fresh water precipitates.

Experimentelle Untersuchung der Ramanstreuung an Kristallpulvern

A comparison of the Raman spectra of single crystals with those made using their powder reveals the following differences: (1) The intensity of the Raman lines decreases with grain size. (2) The breadth of the lines increases with grain size. (3) The spectra of powder specimens show additional lines. The decrease in the intensity is mainly due to surface scattering, whereas the broadening of the lines can be caused by two different factors: (a) In the case of polar crystals different spectra overlap because of different orientations of the grains. (b) Additional interactions with `surface modes' of the individual crystals, which may also show a dispersion depending on the shape of the grains. Na2WO4 with its higher symmetry and the weakly polar SiO2 show the decrease in intensity, while the examples showing the interactions with `surface modes', are quartz and platy crystals of SiC. Anomalous broadening can be demonstrated using strongly polar KIO3. The results of this study have been applied to determining the effect of such lamellar structures, as in labradorites, on Raman lines.

Comparative chemistry of amorphous and apatitic calcium phosphate preparations

Unwashed samples of amorphous calcium phosphate (ACP) contain an irreplaceable labile fraction, rich in acid phosphate and low in Ca/P ratio, which is irreversibly lost during the washing process. Native ACP precipitated in the pH range 6.6–10.6 varied in Ca/P molar ratio from 1.18 to 1.50 and in HPO42−/total P from 33.0% to 10.1%. At pH 7.40, native ACP had a Ca/P molar ratio of 1.36±0.02 and contained 22.8 (±2.2)% HPO42−. Unwashed precipitate data could not be attributed to either trapped supernatant Ca2+ and HPO42− or extraneous Na+, Cl−, and CO32−. The amorphous calcium phosphates are recognized as a class of salts having variable chemical but identical glass-like, physicochemical properties. Non-crystalline CaHPO4·xH2O may also be an ACP, especially during early formative stages. At physiological pH, ACP transforms to small platy crystals containing large amounts of readily-replaceable acid phosphate. Washing this surface layer produced chemical alterations in the resultant crystals; unwashed crystals had poorly-crystalline apatitic diffraction patterns but exhibited poorly-resolved infrared spectra intermediate between apatite and octacalcium phosphate. Structural explanations for all these phenomena are discussed, and revised bone and cartilage amorphous/crystalline mineral compositions have been re-calculated.

Compaction of the Bishop Tuff, California

The foliation in welded tuffs is defined by planar alignment of glass shards, platy crystals, and flattened pumice fragments. The textural features and interrelationships of these elements are clearly the result of the deformation of ash-flow material. The strain involved in developing the alignment can be determined by measuring deformed objects of known original shape. The orientation and shape of the two-dimensional finite strain ellipse, computed from measured bubbles and Y-shaped shards, demonstrates that the long axis parallels the foliation and that there is a close correspondence between the ratio of the principal strains and the bulk density. The measured strain is inhomogeneous on at least two scales. Single cooling units show a regular and continuous vertical variation in deformation: the upper and lower portions are nearly undeformed, whereas the middle portion of the sheet is strongly deformed. On a small scale, the strain varies systematically around rigid lithic fragments and crystals and reaches high ratios at the tops and bottoms of these objects, while pressure shadow zones develop at the sides, which may have complex strain histories. All the lines of evidence point to compaction as the only mechanism involved in the production of the observed characteristic features of the Bishop Tuff, a Pleistocene ash-flow sheet in eastern California. Deformation in the tuff is defined by (1 + e 1 ) = 1.0. During flow and the earliest stages of compaction, pumice lapilli behave as rigid bodies. At about 50 percent porosity, the pumice collapses with the matrix, but at a more rapid rate, and the final forms are flattened in the plane of the foliation. Final shape ratios may reach 25 by simple volume loss; further flattening by essentially volume constant deformation may account for the relatively high mean ratios in fully compacted tuff, and for large ratios reported by others. A comparison of these results with selected specimens of other tuff units and published data strongly suggests that compaction is the dominant mechanism in producing the strong parallel alignment of textural components in all these welded tuffs. In cases where late or postcompactional deformation has also taken place, its effects are superimposed on the earlier compactional features; even so, the results appear to be more closely related to processes in the compactional stage. Extensive flow at or near final tuff densities does not explain most of these features.

Bavenite from Transbaykal

Accumulations of fine platy crystals of bavenite, colorless or white, often with inclusions of graphite, were discovered in an albitized garnet skarn, in a geological environment in which the mineral, a relatively high-temperature metasomatic replacer of phenacite and feldspar, is definitely not an end-stage product of a hydrothermal process. – IGR Staff.

Feitknechtite and its Origin from Noda-Tamagawa Mine, Iwate Prefecture, Japan.

Pyrochroite occurs abundantly as a main ore-forming mineral at the bedded manganese ore bodies of Noda-Tamagawa Mine. The upper part of the deposits has been oxidized by supergene solutions and consists of manganese dioxide minerals and mixture of feitknechtite and hausmannite (so-called hydrohausmannite). On the other hand, feitknechtite occurs rarely in fissures and small faults developed in the bedded ore bodies consists mainly of pyrochorite with a small amounts of hausmannite, rhodochrosite and manganosite. Veinlets of this mineral at -180m level of Kirihata ore body is not at all affected by supergene solutions. It occurs in a aggregates of brownish black platy crystals up to 3mm in diameter and is intimately associated with hausmannite, and observation under the microscope reveals not seldom the fact that this mineral is pseudomorph after pyrochroite. Accordingly, feitknechtite is considered to be hydrothermal alteration product of pyrochroite formed from the hydrothermal solution accompanied by the granitic intrusion. This oxidation from pyrochroite to mixture of feitknechtite and hausamannite will be attributed to the rising of Eh and the decreasing of pH of the hydrothermal solution at later stage of the hydrothermal mineralization.

Zinc Mica from Franklin Furnace, New Jersey

PLATY crystals of a dark mica occur in hancockite-bearing rocks from Franklin Furnace, New Jersey, and electronprobe analysis shows that the mica has high zinc (19.8 per cent) and manganese (12.5 per cent) oxide contents, corresponding to about 40 and 30 per cent respectively of the zinc and manganese end-members. So far as we are aware, no description of such a mineral has previously been published. This communication reports analytical, optical and X-ray data for two samples of the mica, one from the collection of the Department of Mineralogy and Petrology, Cambridge, the other from a hancockite–axinite rock presented by Prof. C. Frondel.

Crystallography of psilomelane, A3X6Mn8O16

SummaryPsilomelane has been redefined from single crystal study to be of orthorhombic symmetry with the space group P222, the dimensions a 9·45, b 13·90, c 5·72 Å, and two molecules of per unit cell, where A represents Ba2+, Mn2+, Al3+, Fe3+, Si4+ etc., and X6 stands for (O,OH)6 with OH about 5. This formula is very closely followed by 14 analyses of psilomelane, and the calculated density agrees fairly well with the observed density. The powder data of psilomelane cannot be indexed with Wadsley's monoclinic cell and the conditions for the space group A2/m, proposed by Wadsley for his crystal, are not satisfied by the indexing. Wadsley's crystal was not psilomelane but probably an altered phase of Vaux's neotype specimen.The electron micrograph of shining platy crystals of psilomelane shows some almost square-faced crystals whereas that of the botryoidal material consists only of particles with irregular edges. The dehydration product of psilomelane shows gradual shrinkage of the orthorhombic cell up to 500° C, marked structural changes at 600° C, and transformation at 800° C to a monoclinic phase, similar to hollandite.

Occurrence of ferberite from Obanazawa Mine, Yamagata Prefecture, and its significances in the mineralization in the green tuff region

The Obanazawa mine is situated about 9.5km north-east of Obanazawa City, Yamagata Prefecture, northeastern Japan. The ore deposit is made up of copper-zinc quartz veins developed in dacite and dacitictuff of Miocene age. Ore minerals are chalcopyrite, sphalerite, pyrite, tetrahedrite and ferberite. The pyrite has either pentagonal dodecahedral form or colloform textures. This is the first occurrence of ferberite in the green tuff region of the inner zone of northeastern Japan. Hexagonal; platy crystals of pyrite are observed in the vein found in the Komatazawa valley. It seems that they were crystallized as pyrrhotite single crystals and altered to pyrite aggregates after the formation of the vein. Gangue mineral is quartz accompanied by a small amount of barite. Argillization (mainly sericitization) and silicification are distinguished. Ferberite was identified by means of X-ray and chemical analysis; the composition is (Fe0.90 Mn0.10)WO4. Occurrence of ferberite and pyrite after pyrrhotite means that the veins may have formed at high temperature but the properties of other vein minerals suggest that they crystallized at low temperature. They have been explained as a telescoping phenomena of xenothermal type deposits in the greentuff region. The Obanazawa mine is situated at the intersection of N-S and NWSE main structural lines of northeastern Japan ; the basement of this area seems to be uplifted. The mineral assemblages of this ore deposit may be explained by assuming that a subvolcanic magma chamber exists in this area.

Electron-optical data for crystals of scarbroite

SummaryElectron micrographs of scarbroite show thin platy crystals of about 1 μ size, having rhombic outlines with angles 66° ± 1° and 113° ± 1°. Single-crystal electron-diffraction patterns show rectangular net patterns, with d100 = 9·90 Å., d010 = 14·67 Å., γ* = 90° ± 0·05°. Strong hk0 reflections show a pseudohexagonal arrangement, but true symmetry is probably orthorhombic or monoclinic. Faces outlining rhombic forms are of type {11l}, .

37. 三重県竹原産モナズ石およびフェルグソン石

Monazite from Takehara, Mie Prefecture is greenish gray brown prismatic or platy crystal with a (100), m (110), v (I11) as principal faces, and sometimes with n (120), e (011), w (101) and x (I01).Fergusonite from same locality is blackish small loose crystal, and sometimes as prismatic one with s (111) and g (320).

Chemical compositions of euxenite and ilmenite from the Ippaiyama pegmatite, Fukushima Prefecture

Main constituent minerals of the pegmatite are microcline perthite, plagioclase, quartz, muscovite and tourmaline. A considerable amount of platy crystal of ilmenite, sometimes attaining to 10cm in diameter and 1cm in thickness, occurs associating with pinkish microcline perthite of which composition is represented as Or68.1 Ab31.4 An0.5. Euxenite, less than 1×3mm in size, is found in close association with ilmenite. The results of chemical analyses of ilmenite and euxenite are shown in the table 2 and 4 respectively. Ilmenite has excessive amounts of Fe2O3 and Ti02 which were derived from the mingling of unmixing hematite and titania mineral (rutile ?). The chemical formula of euxenite is calculated as (Ca0.10 Mn0.01 Th0.02 Ce0.04 Y0.54 U0.16 Fe+20.12)0.99 (Mg0.03 Fe+30.05 Al0.02 Ti1.20 Nb0.43 Ta0.25 Si0.08)2.06 (0, OH)6.34.

35. 北海道鴻ノ舞鉱山産レーメル石

Roemerite from the same locality forms an aggregate of small chest nut brown platy crystals. The identification was also based on the chemical and X-ray characters.

北海道虻田鉱山のクリストバル石

Cristobalite and opal are contained in the wall-rocks (tuff and agglomerate) of the native sulphur and iron sulphides ore deposits, and in the disseminated limonite (goethite) ore of the Abuta Mine in south-western Hokkaido, Japan.These are not found in the massive iron sulphides ore and moss-limonite (goethite) ore that always contains quartz as silica minerals. The x-ray diffraction data show that the cristobalite is mostly α-(low) type. Its hexagonal platy crystal can be found in the electromicrograph.It is considered that the cristobalite has been formed as a secondary mineral from opal which is one of the hydrothermal alteration minerals-alunite, kaolin, montmorillonite, anatase?, pyrite, marcasite, native sulphur, etc. Cristobalite is also found in the wall-rocks of the native sulphur ore deposits of the Tokusyumbetu Mine and in the clay under the moss-limonite (goethite) ore deposit of the Kuttyan Mine.