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69 hits

  • Thumbnail for PS-2b-IG
    PS-2b-IG

    Clinopyroxene and plagioclase crystals with a hypidiomorphic granular texture. Clinopyroxene is cloudy and patchy in appearance due to alteration by a fine-grained material. Alteration by randomly-oriented, feathery chlorite pervades grain boundaries and fractures in the thin section.

  • Thumbnail for SC-6
    SC-6

    The range in grain size for the plagioclase laths in this thin section is continual from the groundmass euhedral microlites to the subhedral phenocrysts. Concentric zoning and sieve textures are common in the plagioclase phenocrysts. Clinopyroxene phenocrysts are also subhedral, commonly twinned, and infrequently clustered in glomeroporhpyroclasts. In addition to plagioclase, the groundmass contains clinopyroxene, opaques, and serpentine.

  • Thumbnail for BATUR 1918
    BATUR 1918

    Subhedral phenocrysts of plagioclase, clinopyroxene, and olivine are scattered randomly throughout this basalt. Plagioclase has a sieve texture and is frequently zoned. The corners of most grains are rounded. Both clinopyroxene and olivine are generally equant in shape and olivine is more abundant than the pyroxene. All three phases show some degree of resorption. The groundmass contains moderately-sized crystals of all three phases. This sample is very fresh and unaltered.

  • Thumbnail for JPN-12
    JPN-12

    This cryptocrystalline basalt consists of a groundmass of plagioclase microlites, equant opaques, glass, and interstitial, anhedral phlogopite. Microphenocrysts of subhedral clinopyroxene comprise the remainder of the sample.

  • Thumbnail for BATUR 94 FL
    BATUR 94 FL

    Sieve textured plagioclase blocks and laths dominate the phenocrystic population in this microporphyritic vesicular basalt. Clinopyroxene phenocrysts are less abundant. Both phases are found with glass as constituents of the groundmass.

  • Thumbnail for 58-K-91
    58-K-91

    Unoriented plagioclase laths and interstitial glass and clinopyroxene make up the groundmass of this vesicular basalt. Olivine and orthopyroxene microphenocrysts are scattered throughout.

  • Thumbnail for JPN-3
    JPN-3

    The olivine that is so conspicuous in the JPN-3 handsample is conspicuously absent in thin section and represented by a mere 1 or 2 grains. Rather, phenocrysts of plagioclase and pyroxenes dominate the phaneritic phases. Both phases are subhedral and the plagioclase in particular indicates several different generations of growth. Some plagioclase is concentrically zoned, though most grains contain alternating inclusion-rich and poor zones. Inclusions are of pyroxenes and glass blebs. The groundmass contains glass, plagioclase microlites, and tiny pyroxenes.

  • Thumbnail for SC-7
    SC-7

    The groundmass of this microporphyritic basalt consists of glass and plagioclase microlites. Subhedral plagioclase phenocrysts are roughly aligned and some are concentrically zoned. Subhedral, plucked, clinopyroxene phenocrysts of variable size are less abundant than those of plagioclase.

  • Thumbnail for 869
    869

    Several glomeroporphyroblasts of clinopyroxene and opaques with hornblende, biotite, and chlorite rims are scattered throughout this syenite. The remainder consists of altered k-feldspars and rare quartz grains with rather sutured grain boundaries.

  • 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 BB13
    BB13

    In thin section, this flow-banded aphanitic rock displays a few fractured and embayed plagioclase and clinopyroxene phenocrysts in a groundmass dominated by aligned microlites of the same two phases. One or two phenocrysts of orthoclase are also present. The microlites define a trachytic texture, which is observable in handsample as flow bands.

  • Thumbnail for JPN-8
    JPN-8

    The groundmass of this porphyritic basalt is comprised chiefly of glass, plagioclase, and clinopyroxene, in decreasing proportions respectively. Some plagioclase phenocrysts have sieve textures, some inclusions of glass blebs, others are concentrically zoned, and still more are relatively fresh. Clinopyroxene phenocrysts frequently form glomeroporphyroclasts, sometimes with olivine; several grains have coronas of differing composition growing around them. Both olivine and clinopyroxene are heavily fractured and irregularly shaped.

  • Thumbnail for KBR8
    KBR8

    Plagioclase and clinopyroxene form subhedral, unaltered grains amongst a background of finer-grained, intermingled iddingsite and zeolites. Iddingsite may be a pseudomorph after biotite. Described by 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 JPN-9
    JPN-9

    The crystals in this thin section look somewhat out of equilibrium with the melt. The groundmass is microcrystalline and riddled with plagioclase and pyroxenes, as well as glass. Crystals of the phenocryst population are generally subhedral, with rounded corners and irregular twins. The pyroxenes are frequently rimmed by pyroxenes of differing composition. Plagioclase phenocrysts are of differing generations; the first has cloudy, inclusion-rich cores with fresh rims and the second lacks this core. Both may be concentrically zoned. The pyroxenes in particular tend to cluster in glomeroporphyroclasts. The occasional granular aggregate of calcite can be observed in this sample.

  • Thumbnail for SC-13
    SC-13

    The least altered phase in this thin section is plagioclase, which forms roughly aligned, variably sized laths that make up both the groundmass, which is dominantly glass, and the phenocryst population. A second phenocryst, clinopyroxene, remains only as inclusions in the calcite pseudomorphs that replaced it. Vesicles, clays, and hematite pseudomorphs are abundant in this thin section.

  • Thumbnail for KBR2
    KBR2

    The dominant texture in this gabbro is an ophitic intergrowth of equant plagioclase laths within larger, subhedral, clinopyroxene grains. Alteration of some phases to chlorite, talc and iddingsite is localized and occurs more in non-ophitic sections of the rock.

  • Thumbnail for JPN-15
    JPN-15

    This inequigranular mosaic of pyroxenes and olivine is highly fractured. Subparallel swarms of high-density fractures are visible throughout and contain the highest concentrations of serpentine. The infilled minerals of one conspicuous vein have a nice comb texture.

  • Thumbnail for 32
    32

    Grain shapes in this thin section tend to be subhedral to anhedral with a great variety in grain size. Lath-shaped plagioclase grains have both albite and Carlsbad twins, while larger, more equant grains show concentric zoning. Other phases in this sample include strongly pleochroic biotite, clinopyroxene, nephaline, orthoclase, and opaques. The clinopyroxene, biotite, and opaques tend to cluster together. Fairly large, euhedral apatite crystals are found throughout.

  • Thumbnail for 15-1
    15-1

    The k-feldspar in this thin section is unaltered and displays albite and tartan twins and beautiful flame lamellae. The grain boundaries between feldspars are often sutured. Interstitial calcite is present. Anhedral and altered hornblende, clinopyroxene, and biotite are distributed randomly throughout.

  • Thumbnail for BB6
    BB6

    Amidst the groundmass of glass, randomly oriented plagioclase laths and equant to anhedral patches of secondary serpentine, are strewn subhedral phenocrysts of plagioclase and twinned clinopyroxene.

  • Thumbnail for KBR5
    KBR5

    Plagioclase is roughly twice as abundant than clinopyroxene in this sample, though where present, clinopyroxene grains are large and encompass multiple inclusions of plagioclase giving a spotty ophitic texture to the gabbro. Iddingsite replacement is extensive and plagioclase is altering to clays. Apatite is found in short stubby prisms, hexagonal cross sections, and long needles.

  • Thumbnail for PS-1b-bs
    PS-1b-bs

    The groundmass of this basalt is composed of plagioclase microlites with tiny interstitial clinopyroxenes. Vesicles are infilled with chlorite and quartz. The few larger plagioclase phenocrysts have been partially altered to calcite.

  • Thumbnail for PS-3a-cpx
    PS-3a-cpx

    Hypidiomorphic, inequigranular clinopyroxene with serpentine-filled fractures and interstices.

  • Thumbnail for BATUR 94 CR
    BATUR 94 CR

    Sieve textured plagioclase blocks and laths dominate the phenocrystic population in this microporphyritic vesicular basalt. Clinopyroxene phenocrysts are less abundant and olivine less abundant still. All three phases are found in the groundmass. Groundmass clinopyroxene and olivine are more abundant than in BATUR 94 FL.

  • Thumbnail for KBR14
    KBR14

    Described by Western Minerals Inc. as 'porphyroblastic metasediments/hybrid rocks, interpreted by Eales and his coworkers as metamorphosed 'Red Beds' Formation sediments but conceivably magmatic in origin. The specimens illustrate the range in textures and compositions.' A common characteristic of all minerals in this thin section is that despite their natural habit, most minerals are elongate and frequently form cross-cutting, disparate but optically continuous, bladed crystals. It appears to be an almost dendritic intergrowth of all phases.