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11 hits

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    504; 505

    The feldspars in this thin section are partially sericitized and somewhat poikilitic and the biotite is substantially altered. Grains are generally anhedral in shape.

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    513

    Square phenocrysts of quartz and feldspar disrupt this porphyritic granite's otherwise mosaic of equigranular grains. Subhedral and partially resorbed biotite is scattered throughout.

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    unknown-71

    Unaligned, prismatic crystals of schorl, with strongly mauve to indigo pleochroism and concentric compositional zoning are scattered throughout the sample. Basal sections remain a deep blue regardless of rotation of the stage. A corona of clear tourmaline (perhaps) rims most grains. The tourmaline are found in a sericitized feldspars.

  • Thumbnail for BB35
    BB35

    Grain boundaries between the anhedral quartz and k-feldspar grains in this sample are framed with myrmekitic intergrowths. These intergrowths even appear in plane polarized light due to the high degree of feldspar alteration to clay. The mica phases are sparsely distributed and small in size.

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    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 497
    497

    Though dominated by k-feldspar, albite and quartz, this thin section contains biotite pseudomorphs after hornblende, and trace monzaite (distinguished by its high relief, high birefringence colors, and square to diamond shape).

  • Thumbnail for BB33
    BB33

    This sample has a classic, medium-grained, granitic texture. Grains are generally comparable in size and shape is typically subhedral to anhedral. Biotite is anhedral and weakly pleochroic.

  • Thumbnail for 679
    679

    This allotriomorphic granite is dominated by feldspar phases which are altering to clays. The mica phases are anhedral, emabyed, and filled with unaligned opaque inclusions.

  • Thumbnail for 876
    876

    The riebeckite grains in this sample are embayed in a skeletal fashion, with embayments strongly controlled by the amphibole cleavage. The feldspars have classic albite and tartan twins in addition to patchy lamellae.

  • Thumbnail for 498
    498

    This sample is quite coarse-grained. Tartan twinning in the k-feldspar is overprinted by flame and blebby lamellae and both are riddled with inclusions of hornblende, micas, and monazite or zircon. Radiation halos are found around the zircons or monazite crystals found as inclusions in biotite grains.

  • Thumbnail for 502
    502

    This fine-grained granite has a mosaic texture. The quartz seems undisturbed, however, most other phases display evidence of weathering and disequilibrium. The dusting of clays and presence of sericite inclusions in the feldspars indicates they are chemically weathered. Biotite and muscovite are skeletal in appearance and biotite is frequently interfingered with chlorite.