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92 hits

  • Thumbnail for 6
    6

    The three essential felsic species occur in two sizes. The larger plaioclases are euhedral and zoned and are pheocrysts, in places glomeroporphritic. A few large subhedral kaolinized orthoclase grains are present as are large quartz anhedra. These are set in a poorly defined groundmass of variable grained quartz, orthoclase, plagioclase, biotite, and hornblende. Of these the mafics are subhedral, the plagioclase is euhedral, and the others anhedral. Hornblende, more strongly altered than biotite, is variably colored in pale green, bluish green and buff. It is replaced by chlorite and epidote. Accessories are magnetite, apatite, sphene and zircon.

  • Thumbnail for JN-01
    JN-01

    Moderately aligned hornblende prisms dominate this rock and give it its green color. Interspersed among the hornblende is a granular matrix of quartz and k-feldspar. Biotite and epidote appear periodically. The layering in this thin section is controlled by variation in grain size of the hornblende minerals.

  • Thumbnail for 990
    990

    The minerals in this sample all appear to intergrow with one another. Most grain boundaries are lobate, especially between feldspar phases and flame lamellae and perthitic intergrowths abound. Although a few hornblende crystals are euhdral in shape, the majority are found as rims around possible clinopyroxene or olivine grains and they tend to group with the other mafic phases. Euhedral apatite appear throughout.

  • 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 23-5A
    23-5A

    A continuous foliation defined by aligned euhedral biotite characterizes this fine-grained sample. Granoblastic quartz and feldspars fill the voids between biotite crystals. Small, equant opaqes are distributed evenly throughout.

  • Thumbnail for ERB-0X3
    ERB-0X3

    In this sample, a spaced, anastamosing schistoscity defined by biotite, garnet, hornblende and opaques wraps around deformed feldspar lenses which display undulose extinction and bent growth as well as deformation twins. Polyganized quartz and feldspar mantles the feldspar porphyroclasts. Quartz ribbons are prevalent throughout this sample. The sense of shear is ambiguous.

  • Thumbnail for SS-3674-1
    SS-3674-1

    Subhedral biotite and uralitized augite crystals are the prominent mafic phases in this sample, though olivine is also present in lesser amounts and as an inclusion in one of the two other mafic phases. K-feldspar, zeolites, and apatite are the primary leucocratic constituents. There is a good deal of intergrowth between and alteration of minerals in this thin section.

  • Thumbnail for SS-3674-5
    SS-3674-5

    This is a very hypidiomorphic coarse-grained sample consisting of large grains of augite, frequently intergrown with opaques, and intergrown k-feldspar and nephaline. Augite is found altering to biotite. Radiating splays of zeolite are present to varying degrees within the three copies of this thin section.

  • Thumbnail for BB3
    BB3

    Large, euhedral to subhedral plagioclase blocks are in far greater abundance than either k-feldspar or quartz, both of which are anhedral in shape. All the ferromagnesian phases are anhedral in shape and tend to cluster together. Hornblende growth is at the expense of clinopyroxene. Opaques cluster with the ferromagnesian phases. Quartz displays first-order yellows in this slightly thickened sample.

  • Thumbnail for 504; 505
    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.

  • Thumbnail for 21-4
    21-4

    The foliation in this coarse-grained rock is the result of compositional layering; discontinuous hornblende-rich zones separate poikiloblastic plagioclase-rich regions. Albite and Carlsbad twins in the feldspars are almost entirely obscured by randomly-oriented inclusions of sericite.

  • Thumbnail for SS-3674-8
    SS-3674-8

    A few biotite phenocrysts punctuation this sample's fine-grained groundmass of unoriented elongate biotite, k-feldspar, nephaline crystals and anhedral calcite masses.

  • Thumbnail for SC-15
    SC-15

    This fine-grained, hypidiomorphic, inequigranular plutonic rock is intermediate in composition, with plagioclase as the dominant feldspar. K-feldspar is present in much lower abundance, and quartz is scarce. Mafic phases include anhedral biotite and hornblende, the latter of which is strongly chloritized.

  • Thumbnail for SYH-1GG
    SYH-1GG

    The fabric in this thin section is more disordered than others from this suite. All phases commingle and an alignment of elongate phases amidst many equant phase forms a weak foliation. Garnet and omphacite form porphryclastic, poikiloblastic grains.

  • Thumbnail for ERB-02
    ERB-02

    This sample is a strongly mylonitized pelitic schist with a continuous schistoscity defined by strongly alligned biotite, fibrous sillimanite, and opaques and interspersed with discontinuous quartz and k-feldspar ribbons. K-feldspar is strongly sericitized. The sense of shear is ambiguous.

  • Thumbnail for 884
    884

    The flame lamellae that pervade this thin section are cut thicker than ususal and thus display first order yellows and oranges, though the tartan twinning of the microcline retains the ususal first order grey birefringence. Grain boundaries between feldspars are lined with smaller feldspar grains, which gives the larger grains a scalloped appearance. The hornblende grains are highly irregular in shape and contain many inclusions of feldspar, opaques, biotite, and other unidentifiable phases.

  • Thumbnail for 878
    878

    Grain shapes in this thin section are consistantly anhedral. Weathering of the feldspars give them a dusty appearance. Because the thin section is cut too thick, the birefringence of quartz and some k-feldspars is as high as second order blues. Mnay hornblende crystals are nearly opaque and they are frequently found surrounding and likely replacing inclusions of pyroxene (perhaps). The biotite and hornblende are rather skeletal. Euhedral sphene and apatite are occasionally scattered throughout.

  • Thumbnail for 877
    877

    This generally allotriomprhic-equigranular thin section is thicker than standar thin sections, thus the quartz and some k-feldspar grains display first order red to pink colors. The riebeckite is nearly opaque in both plane and cross-polarized light.

  • Thumbnail for 18-9
    18-9

    The layering in this fine-grained amphibolites is defined by bands of amphibole alternating with granoblastic quartzofeldspathic layers. Granular aggregates of epidote are dispersed randomly throughout the rock. Fractures cross-cutting and off-setting the layering are more visible with the naked eye then under the microscope, though one fracture (with no offset) is filled with a seam of epidote. A couple of porphyroclastic and poikiloblastic chlorite grains are clearly truncated by the fractures.

  • Thumbnail for BB18
    BB18

    This fine-grained granite contains abundant feldspars, many of which display concentric zoning from plagioclase cores to k-feldspar rims. Biotite grains are altering to and interfingered with chlorite. Rounded hornblende crystals are rare in this sample.

  • Thumbnail for 872
    872

    The feldspar grains in this thin section span a broad range of sizes, with larger grains displaying strong lamellae of either the blebby or flame variety. The mafic phases are anhedral to skeletal in shape and are much less abundant than the more felsic phases. The minerals in this thin section are highly fractured lending the appearance of porousness to this intrusive igneous rock.

  • Thumbnail for 513
    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.

  • Thumbnail for 544
    544

    Although the bulk of this thin section has an aplitic texture of quartz and feldspar, several larger feldspar phenocrysts punctuate the mosaic texture of the smaller population of quartzofeldspathic phases. Biotite is sparse and where present, skeletal in shape.

  • 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 23-6K
    23-6K

    A foliation defined by aligned hornblende is cross-cut by a seam running from the upper-left to lower-right of the thin section. The seam is coarse-grained and unfoliated with a quartzofeldspathic margin and grains of resorbed, subhedral clinopyroxene in the middle.