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13 hits

  • 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 KBR1
    KBR1

    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 clays is localized and occurs more in non-ophitic sections of the rock.

  • 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 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 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 PS-3a-occp
    PS-3a-occp

    Olivine clinopyroxenite cumulate with postcumulus (intercumulus) plagioclase.

  • 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.

  • 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 KBR2A
    KBR2A

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

  • 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-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 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 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.