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23 hits

  • Thumbnail for SS-3674-6
    SS-3674-6

    This porphyritic sample contains phenocrysts of augite, olivine, and pseudoleucite. Olivine has an iddingsite rim when in contact with the groundmass. The pseudoleucite phenocrysts are a colorless and cloudy, roundish eight-sided crystals with first-order grey birefringence and extinction occurs in amoeboid-shaped sections within the phenocryst. These same pseudoleucite crystals make up the majority of the groundmass, along with calcite, k-feldspar and other alteration products. Three copies of this thin section contain the contact zone itself, with a calcite and clay-rich, layered Eagle sandstone.

  • 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 SW6
    SW6

    Large, anhedral, interlocking crystals of olivine and clinopyroxene are found in this coarse-grained rock. Olivine alteration to iddinsite is confined to fractures which pervade the rock and cross-cut both mineral phases. Perthitic pyroxene intergrowths are observed. A contact between an ore-rich, opaque zone and the peridotite is preserved in the thin section.

  • Thumbnail for KBR9
    KBR9

    Plagioclase and clinopyroxene form subhedral and anhedral grains, respectively, though unlike the other ferrotholeiites in this suite, both are cross-cut by or being pseudomorphed by iddingsite, a very dominant mineral in this thin section. Interstitial, undeformed quartz is found in the groundmass and inclusions of apatite crystals lend an almost graphic texture to this phase. 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 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 KBR2A
    KBR2A

    This gabbro has a subophitic texture. Alteration to chlorite and iddingsite occurs mostly between grain boundaries.

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

    Olivine clinopyroxenite cumulate with postcumulus (intercumulus) plagioclase.

  • Thumbnail for KBR7
    KBR7

    Plagioclase and clinopyroxene form subhedral, unaltered grains amongst a background of finer-grained, intermingled iddingsite and zeolites. 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 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 KBR3
    KBR3

    The clinopyroxene abundance in this thin section is lower than other gabbros from Birds River, lending more of a subophitic texture to the rock. Plagioclase is the most dominant mineral. Iddingsite is less abundant.

  • 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 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 SS-13
    SS-13

    This porphyroclastic thin section has a groundmass dominated by k-feldspar and zeolites, though other phases may be present in lesser amounts. The phenocrysts are euhedral augite and olivine, which are frequently found clustered together in glomeroporphyroclasts. The olivine is consistently rimmed by iddingsite and the augite frequently displays concentric zoning. Tiny crystals of equant apatite and rounded opaques thoroughly pepper the thin section.

  • 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 CM3
    CM3

    Augite and olivine are the two crystalline phases in this 'cloudy' vesicular basalt. Iddingsite replacement of olivine is almost comprehensive; commonly, iddingsite nodes are the only indication of olivine's presence. The groundmass is microcrystalline and altered enough as to be unidentifiable.

  • 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 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 881
    881

    This gabbro is altered to the point of being nearly unrecongnizable. All primary phases are obsecured secondary mineralization. Clays have replaced the plagioclase grains and mats of chlorite and iddingsite, with some minor biotite are found clustered around the euhedral opaques. Overprinting all of this are euhderal apatite grains that range up to nearly a centimeter in length.

  • Thumbnail for CM2A
    CM2A

    Augite and olivine are the two predominant crystalline phases in this vesicular basalt and define a microporphyritic fabric. Iddingsite replacement of olivine is minimal. As smaller crystals, both phases, along with opaques, a feldspar, and glass, comprise the groundmass.

  • 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 CM2A
    CM2A

    Augite and olivine are the two predominant crystalline phases in this vesicular basalt and define a microporphyritic fabric. Iddingsite replacement of olivine is minimal. As smaller crystals, both phases, along with opaques, a feldspar, and glass, comprise the groundmass.

  • Thumbnail for SC-4-BL
    SC-4-BL

    Phenocrysts of plagioclase, clinopyroxene, and iddingsite pseudomorphs after olivine–presumably–are surrounded by a groundmass of unoriented plagioclase microlites, glass, and localized calcite. Plucking of the phenocrysts is noticable and vesicles are present.

  • Thumbnail for KBR6
    KBR6

    Though clinopyroxene and plagioclase were undoubtedly once more abundant in this gabbro, subsequent alteration has left radiating zeolites, a cloudy film of clays, and veinlets and pseudomorphs of iddingsite the dominant minerals in this thin section.