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13 hits

  • Thumbnail for 866
    866

    The feldspars in this granite are altering to clays and thus have a consistantly cloudy appearance. The indented grain boundaries in this sample indicate the mutual interference of all phases during growth. The anhedral shape of muscovite grains indicates it grew in the interstices between grains.

  • 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.

  • Thumbnail for 52
    52

    Microscopically mainly cryptocrystalline and merely translucent in shades of gray-brown. Subordinate silty quartz grains, feldspar pieces, sericite flakes, calcite rhombs, and a few particles of pyrite, zircon, magnetite and leucoxene. The dark matrix is composed mainly of illitic clay material.

  • Thumbnail for 868
    868

    The coarseness of this granite obscures in thin section the graphic texture so evident in handsample. The feldspars contain inclusions of muscovite as well as zircon (or another like mineral) and untwinned grains are readily distinguished from quartz by the comprehensive dusting of clay minerals due to weathering.

  • Thumbnail for LS-02b
    LS-02b

    The bulk of this sample is composed of microcrystalline limestone interspersed with calcite rhombs and transected by veinlets of clay and coarse-grained calcite.

  • 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 LS-04a
    LS-04a

    Poorly-sorted, angular, clast-supported, arkosic conglomerate with large clasts of deformed quartz and microcline. Many feldspar grains are altering to clays. Deformed micas are interspersed throughout. Perthite and scotch-plaid twins are extensive. The cement is comprised of microcrystalline quartz and locally, calcite.

  • Thumbnail for LS-02a
    LS-02a

    The bulk of this sample is composed of microcrystalline limestone interspersed with calcite rhombs and transected by veinlets of clay and coarse-grained calcite. According to the collectors, this sample was collected because of its replacement textures.

  • 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 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 LS-04b
    LS-04b

    This moderately-sorted, clast-supported, angular, micaceous sandstone is cemented with microcrystalline quartz and localized calcite. A red hematite stain pervades the sample and concentrates along weathered feldspars. The elongate micas are warped and decaying.

  • Thumbnail for LS-07a
    LS-07a

    This well-sorted, subrounded, chert-cemented quartz sandstone contains alternating clay-rich and poor layers. Accessory minerals and microcrystalline calcite are concentrated along the clay or hematite-rich layers. Hematite concretions and veinlets are found in this sample.

  • 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.