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53 hits

  • 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 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 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 A-6-8B
    A-6-8B

    This sample is an almost monomineralic hornblende amphibolite with trace occurances of poikiloblastic orthoclase and biotite. Biotite growth concentrates along the margins of a high relief, clear mineral with fifth-order birefringence, extreme enough that the inclusions appear to not go extinct. Rarely are radiaiton halos observed in hornblende crystals.

  • Thumbnail for 25-2
    25-2

    The hornblende crystals in this thin section are prismatic and subhedral to euhedral in shape. They are strongly aligned. Filling in between the amphiboles are altered feldspars, granular epidote crystals and euhedral apatites.

  • Thumbnail for BB2
    BB2

    This hypidiomorphic, equigranular monazite has a classic granitic texture with a mosaic of grains all crystallizing simultaneously and impinging on one another's growth. Hornblende is particularly abundant and generally in contact with some combination of biotite, chlorite, and opaques. Some plagioclase grains are concentrically zoned.

  • Thumbnail for A-18-6B
    A-18-6B

    The subhedral hornblende crystals in the sample align with the micas to form a spaced foliation separating microlithons of plagioclase and quartz. Equant subhedral epidote crystals punctuate the rock. Biotite and chlorite are typically interfingered and chlorite display anomalous blue interference colors. Elongate granular aggregates of light brown to colorless titanite are present.

  • Thumbnail for 27-2A
    27-2A

    A continuous foliation in this sample is defined by aligned hornblende grains. Altered biotites are poikiloblastic and have kink bands causing undulose extinction. The aligned hornblende grains are juxtaposed against equigranular polygonal-interlobate quartz and aggregates of altered and decussate muscovite and clinozoisite.

  • Thumbnail for BB8
    BB8

    Large k-feldspar and quartz crystals provide a backdrop for the smaller, less well-preserved mafic phases in this sample. Decomposing biotite is frequently found interfingered with chlorite. Hornblende grains are rather skeletal. Plagioclase crystals have relatively rounded corners and tend to cluster together. Large anhedral aggregates of sphene are interspersed in the interstices between k-feldspar grains.

  • Thumbnail for A-6-7
    A-6-7

    A continuous foliation for this sample is defined by aligned hornblende, micas, elongate quartz grains and granular aggregates of epidote and clinozoisite. Quartz is either equant or elongate with a granular texture. The hornblende phase is generally subhedral in shape, as are biotite crystals, which appear to be pseudomorphing an earlier mineral phase as evidenced by abundant inclusions. Radiation halos can be found in this sample though their occurrance is rare.

  • Thumbnail for PS-2a-pgr
    PS-2a-pgr

    A granitic inequigranular diorite with graphically intergrown, sericitized k-feldspar and quartz, and chloritized hornblende. Clinozoisite and sphene are accessory minerals found throughout the thin section.

  • Thumbnail for BB1
    BB1

    The two feldspar phases in this medium-grained, hypidiomorphic syenite are found in roughly equal abundance, though the plagioclase grains are subhedral to the k-feldspar's anhedral shape, and typically displays concentric zoning. Minor myrmekitic intergrowths between quartz and plagioclase are found between feldspar contacts. Both biotite and hornblende have highly irregular grain shapes.

  • Thumbnail for SC-18
    SC-18

    The fine-grained groundmass in this sample consists of indistinguishable quartzofeldspathic phases. Phenocrysts both feldspar phases are clustered together; the cores of most are absent, perhaps due to plucking during the making of the thin section or possibly due to resorption. Hornblende phenocrysts are very incomplete and anhedral. Biotite phenocrysts are much smaller and subhedral in shape.

  • 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 KBR18
    KBR18

    Elongate plagioclase laths with interstitial clinopyroxene and minor interstitial hornblende and biotite. Classic diabasic texture. Said by Western Minerals Inc. to be the youngest dolerite body in the area and was emplaced at much deeper crustal levels than the gabbros.

  • 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 25
    25

    Highly sericitized subhedral feldspars comprise the bulk of this thin section. Anhedral quartz fills in interstices between feldspar grains. Chlorite pseudomorphism of hornblende is prevalent and biotite alteration, chloritization, and embayment indicates of it too, was out of equilibrium with the melt. Euhedral titanite is found throughout.

  • 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 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 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 15-1
    15-1

    The k-feldspar in this thin section is unaltered and displays albite and tartan twins and beautiful flame lamellae. The grain boundaries between feldspars are often sutured. Interstitial calcite is present. Anhedral and altered hornblende, clinopyroxene, and biotite are distributed randomly throughout.

  • Thumbnail for 871
    871

    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. Small zircon crystals are clustered with a hornblende aggregate.

  • 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.

  • Thumbnail for SC-16
    SC-16

    The groundmass in this thin section is a salt-n-pepper mixture of fine-grained, amorphous quartzofeldspathic phases. All phenocryts are subhedral in shape, and the largest of these, the k-feldspar and plagioclase are host to abundant hematite-filled fractures. Biotite and hornblende phenocrysts are much smaller. A few spherulites, seen more clearly in plane than cross polarized light, are found in the groundmass.

  • Thumbnail for JPN-17
    JPN-17

    The majority of this thin section is a mosaic of inequigranular, anhedral hornblende and highly-poikilitic k-feldspar. Though a few large, irregularly shaped masses of prehnite are interspersed amidst the hornblende and k-feldspar, most prehnite is concentrated along a single vein that runs the length of the thin section. Some of the prehnite shows anomalous blue extinction.