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69 hits

  • Thumbnail for PS-2d-troc
    PS-2d-troc

    Allotriomorphic plagioclase and highly-fractured olivine are the dominant minerals in this thin section. Clinopyroxene, when present, is found adjacent to olivine. Fractured zones in this rock follow olivine clusters and frequently cross-cut plagioclase crystals in swarms between nodes of granular olivine.

  • Thumbnail for PS-3a-occp
    PS-3a-occp

    Olivine clinopyroxenite cumulate with postcumulus (intercumulus) plagioclase.

  • Thumbnail for KBR11
    KBR11

    Like KRB10, plagioclase and clinopyroxene are intergrown in an almost graphic texture, though where KRB10 was dominated by the unknown mineral, in KRB11, that unknown mineral is confined to spherulite-like clusters in a fine-grained quartz matrix. Iddingsite alteration is much less extensive. 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 KBR4
    KBR4

    Plagioclase and clinopyroxene abundances are lower in this gabbro compared to others of Birds River. Radiating splays of zeolites with serpentinized margins, as well as iddingsite and chlorite replacement of an equant mineral phase contributes nearly half the bulk of the thin section.

  • Thumbnail for SC-19
    SC-19

    The grain size of plagioclase laths in this porphyritic basalt ranges continuously from the groundmass microlites to milimetric phenocrysts. Glass and sparse equant pyroxenes comprise the remainder of the groundmass. Clinopyroxene phenocrysts are patchy due to plucking.

  • Thumbnail for SC-10
    SC-10

    The salt-n-pepper groundmass of opaques, pyroxenes, and feldspars appears almost intserstitial due to the high abundance of microphenocrysts. The phenocrystic population is dominated by subhedral plagioclase and, to a much lesser degree, clinopyroxene. Rounded, phenocryst-sized pockets of granular quartz are found throughout the groundmass.

  • Thumbnail for JPN-1
    JPN-1

    The phenocrysts in this basalt are plagioclase, orthopyroxene and clinopyroxene. Most pyroxenes are gathered in glomeroporphyroclasts with plagioclase, though the latter phase is most commonly found as isolated, irregularly twinned and shaped phenocrysts. The groundmass is glass and plagioclase.

  • Thumbnail for AGUNG FL
    AGUNG FL

    The plagioclase crystals in this vesicular basalt display a continuous range of sized from groundmass microlite to sieve-textured, sometimes zoned blocky phenocrysts. The groundmass contains more blocky plagioclase than other lavas from the Bali suite. The pyroxenes are generally subhedral and form glomeroporphyroclasts.

  • 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 KBR2A
    KBR2A

    This gabbro has a subophitic texture. Alteration to chlorite and iddingsite occurs mostly between 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 PS-3a-PW
    PS-3a-PW

    Serpentine comprises the bulk of this thin section, with skeletal masses of clinopyroxene and isolated granules of olivine dotting the characteristic serpentine mesh-work. The pyroxenes are larger and more complete than the olivine crystals.

  • 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-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 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 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 JPN-7
    JPN-7

    Although labeled an andesite on the sample record sheet, the presence of olivine and absence of hydrous mafic phases in this thin section indicate it is more basaltic in composition. Texturally, it is characteristic of a basalt as well, with a glassy and plagioclase-rich groundmass and phenocrysts of plagioclase, both pyroxenes and olivine. All phenocrysts are subhedral and plagioclase contains inclusions of glass.

  • 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 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 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 JPN-14
    JPN-14

    Texturally, this thin section still resembles a gabbro, with the exception of several talc and serpentine filled veins cross cutting the otherwise equigranular mosaic of clinopyroxene and olivine.

  • 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 1936
    BATUR 1936

    Subhedral phenocrysts of plagioclase, clinopyroxene, and olivine are squeezed into the fine web of rock that rims the massive vesicles of this scoria. 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 22
    22

    Most phases in this thin section are subhedral to anhedral in shape. The k-feldspar have patchy exsolution textures. Most other phases are sparsely distributed and generally subhedral to anhedral.

  • Thumbnail for 867
    867

    This mineral phases in this gabbro are highly fractured and frequently embayed. The pyroxenes are roughly euhedral in shape and several equant grains are twinned. The opaques in this sample are typically equant in shape and contain inclusions of olivine or a fiery orange-red mineral that appears the same in plane- and cross-polarized light.