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123 hits

  • Thumbnail for 6
    6

    The three essential felsic species occur in two sizes. The larger plaioclases are euhedral and zoned and are pheocrysts, in places glomeroporphritic. A few large subhedral kaolinized orthoclase grains are present as are large quartz anhedra. These are set in a poorly defined groundmass of variable grained quartz, orthoclase, plagioclase, biotite, and hornblende. Of these the mafics are subhedral, the plagioclase is euhedral, and the others anhedral. Hornblende, more strongly altered than biotite, is variably colored in pale green, bluish green and buff. It is replaced by chlorite and epidote. Accessories are magnetite, apatite, sphene and zircon.

  • Thumbnail for 671
    671

    This allotriomorphic granite shows evidence of weathering as most feldspars are partially obscured by a dusting of clay minerals. Tartan twinning of microcline is obvious throughout the sample. The curving of biotite cleavage and subhedral grain shapes indicates the biotite is not pristine. It is commonly found occurring with subhedral hornblende as well as large, clear to light brown, anhedral sphene crystals.

  • Thumbnail for 174
    174

    This coarse-grained sample is dominated by anhedral and undulatory quartz and feldspar grains. Subgrains are observed in both phases. The birefringence of both quartz and feldspar are somewhat higher than usual, with both phases exhibiting lower first-order yellows and oranges. An isolated occurance of riebeckite is found at the far edge of one thin section and displays excellent amphibole cleavage and characteristic blue to yellow-green pleochroism. The other copies have highly altered purple-blue pleochroic minerals with indistinct cleavage.

  • Thumbnail for 504; 505
    504; 505

    The feldspars in this thin section are partially sericitized and somewhat poikilitic and the biotite is substantially altered. Grains are generally anhedral in shape.

  • Thumbnail for 497
    497

    Though dominated by k-feldspar, albite and quartz, this thin section contains biotite pseudomorphs after hornblende, and trace monzaite (distinguished by its high relief, high birefringence colors, and square to diamond shape).

  • Thumbnail for 679
    679

    This allotriomorphic granite is dominated by feldspar phases which are altering to clays. The mica phases are anhedral, emabyed, and filled with unaligned opaque inclusions.

  • Thumbnail for 875
    875

    The quartz and feldspar grains in this thin section have rather amoeboid, though elongated shapes. These elongated grains are roughly aligned giving this syenite a somewhat layered appearance. Feldspar intergrowths are primarily of the flame lamellae variety. Rare biotite grains are observed.

  • Thumbnail for J-19-10
    J-19-10

    Although stored with a series of amphibolites, this hornblende-bearing granodiorite preserves more igneous textures than metamorphic. This hypidoimorphic sample consists of equigranular feldspars, randomly oriented, euhedral biotites, and rather anhedral hornblendes grains. Small, rounded, colorless but dusty crystals of titanite are distrubuted throughout the specimen.

  • Thumbnail for BB29
    BB29

    The four phenocrystic phases in this thin section all display disequilibrium textures. Tabular plagioclase pheoncrysts are oscillatorily-zoned at the core and surrounded by as many as three distinct, cloudy, inclusion-rich rims. Quartz phenocrysts are rounded by resorbtion; thick coronas of calcite and hematite pepper, though do not entirely replace, their rims. Relict biotite phenocrysts, pseudomorphed by an opaque phase, are recognized more readily by the consistant rectancular and hexagonal shape than by the rare inclusion of the residual 'host'. These grains, frequently clustered together, have thick black rims and are sometimes infilled with a calcite-like mineral. This calcite-like mineral, frequently found replacing the biotite and as part of the quartz phenocryst coronas, is also observed pseudomorphing a tabular-shaped mineral found both as a phenocryst and part of the groundmass. The calcite seems to be replacing rectangular serpentine phenocrysts, presumably, pyroxene pseudomorphs themselves. The trachytic groundmass consists predominantly of microlites of plagioclase, prismatic opaques, glass, and the periodic rectangular calcite pseudomorph. Granular hematite veins cross-cut the thin section.

  • Thumbnail for CF1B
    CF1B

    The olivine phenocrysts in this vesicular basalt are unaltered, in contrast to the second phenocrystic phase, plagioclase, which has a speckled, mottled alteration texture encroaching concentrically inwards from the grain boundaries. Only the cores and a thin corona of plagioclase on the outermost edges of the phenocrysts remains unaltered by this opaque phase. The glassy groundmass contains of unoriented plagioclase microlites and tiny olivine crystals. Olivine phenocrysts are smaller and less abundant in CF1B than CF1A. Plucking of olivine crystals is extensive.

  • Thumbnail for BB8
    BB8

    Large k-feldspar and quartz crystals provide a backdrop for the smaller, less well-preserved mafic phases in this sample. Decomposing biotite is frequently found interfingered with chlorite. Hornblende grains are rather skeletal. Plagioclase crystals have relatively rounded corners and tend to cluster together. Large anhedral aggregates of sphene are interspersed in the interstices between k-feldspar grains.

  • Thumbnail for BB12
    BB12

    This medium-grained phaneritic rock contains an equal ratio of plagioclase to clinopyroxene grains. Much of the plagioclase is strongly sericitized and several grains are concentrically-zoned. The clinopyroxenes are frequently twinned, heavily-fractured, riddled with inclusions, and show low degrees of alteration to chlorite and serpentine. The pyroxene cleavage is prominent in this sample. Chlorite, serpentine, iddingsite, biotite, and opaques tend to cluster in randomly oriented mats, where chlorite and serpentine growth are often at the expense of biotite.

  • Thumbnail for BB27
    BB27

    A notable feature of this thin section are the large, equant and tabular, concentrically-zoned plagioclase phenocrysts with accumulations of k-feldspar around the margins. The quartzofeldspathic phases within the groundmass of the sample are subhedral in shape, often exhibiting rather cuspate-lobate grain boundaries. Subhedral biotite is scattered throughout the sample, though it frequently clusters with chlorite, calcite, and opaques in greenish aggregates, which appear in handsample as green phenocrysts.

  • Thumbnail for CM4
    CM4

    The vesicles in this microporphyritic vesicular basalt are substantially smaller than the other Carr Mountain samples, though composition remains similar. More calcite permeates the groundmass, in which plagioclase microlites are visible. Unaltered augite and olivine microphenocrysts are observed. An isotropic zeolite, presumably analcite, is seen infilling several vesicles.

  • Thumbnail for CM-incl
    CM-incl

    The layering in this thin section is defined by an opaque phase. Vesicles are pervasive throughout the rock and due to their abundance, the phenocrysts of olivine, pyroxene and feldspar appear to float freely on the slide. Epidote crystals are found among the opaque layers. The rock has a overall cloudy appearance.

  • Thumbnail for 102
    102

    This fine-grained dacite has a strongly cloudy appearance throughout, as well as a film on the surface of the slide that prevents clear focusing. Dusty plagioclase, plucked hornblende, and equant augite are the dominant phases. Euhedral apatite crosscuts most samples. Zeolites and calcite fill most voids or interstices.

  • Thumbnail for ERD3
    ERD3

    This strongly layered rock is also strongly altered and microcrystalline enough for minerals to be indistinguishable. The layering is defined by alternating dark and light lenses. Frequently, elongated, flattened vesicles will have a lighter-colored rim. This thin section has a greasy-looking film on the surface that makes it difficult to focus clearly.

  • Thumbnail for PS-2c-lg
    PS-2c-lg

    Granular, inequigranular gabbro containing occasional olivine crystals. Serpentine is localized to fractures. Grain shapes are very rounded and amorphous.

  • Thumbnail for KBR10
    KBR10

    The unknown mineral is the prominent mineral in this thin section. It forms a dusty brown, isotropic matrix with a faint dendritic texture in which subhedral clinopyroxene and plagioclase grains are set. Clinopyroxene, where isolated, is strongly altered to iddingsite. The degree of alteration is much lower where plagioclase and clinopyroxene grains are intergrown. The two minerals have an almost graphic intergrowth texture. Western Minerals Inc. as an 'interstitial ferrotholeiite, very highly fractionated…textures are similar to those associated with rapidly frozen or highly viscous melts.'

  • Thumbnail for 515
    515

    This hypidiomorphic inequigranular granite has rather scalloped grain boundaries, particularly among the quartzofeldspathic phases, though the biotite grains exhibit similar textures with the feldspars. One anhedral biotite grain has bulbs protruding into the neighboring k-feldspar grain. Quartz extinction is uniform. Olivine is present in trace amounts and the highly-fractured phase is typically surrounded by a thick rim of iddingsite.

  • Thumbnail for 876
    876

    The riebeckite grains in this sample are embayed in a skeletal fashion, with embayments strongly controlled by the amphibole cleavage. The feldspars have classic albite and tartan twins in addition to patchy lamellae.

  • Thumbnail for 498
    498

    This sample is quite coarse-grained. Tartan twinning in the k-feldspar is overprinted by flame and blebby lamellae and both are riddled with inclusions of hornblende, micas, and monazite or zircon. Radiation halos are found around the zircons or monazite crystals found as inclusions in biotite grains.

  • Thumbnail for 877
    877

    This generally allotriomprhic-equigranular thin section is thicker than standar thin sections, thus the quartz and some k-feldspar grains display first order red to pink colors. The riebeckite is nearly opaque in both plane and cross-polarized light.

  • Thumbnail for 871
    871

    The feldspar grains in this thin section span a broad range of sizes, with larger grains displaying strong lamellae of either the blebby or flame variety. The mafic phases are anhedral to skeletal in shape and are much less abundant than the more felsic phases. Small zircon crystals are clustered with a hornblende aggregate.

  • Thumbnail for BB21
    BB21

    A groundmass of glass, clay, calcite, indiscernible quartzofeldspathic crystals, and small, spherical aggregates of chalcedony dominate this sample. Phenocrysts of biotite and calcite pseudomorphs after plagioclase (presumably) comprise the phaneritic crystal population.