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151 hits

  • Thumbnail for ERB-12
    ERB-12

    This two-pyroxene, hornblende-bearing gabbro is highly fractured and has a much finer-grained population of pyroxenes growing in the interstices between larger pyroxene grains. A thin band of finer-grained pyroxne and plagioclase cross-cuts the sample.

  • Thumbnail for 49
    49

    A uniformly fine-grained parallel-oriented aggregate of angular quartz grains, feldspar fragments, chlorite flakes, sericite flakes and shreds, aggregates of submicroscopic clay minerals (chiefly kaolinite), and carbonaceous shreds. Accessory detrital species recognizable are biotite, apatite, zircon, epidote, and tourmaline.

  • 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 ERB-08
    ERB-08

    This thin section contains two main zones. One half contains subhedral grains of k-feldspar, quartz, orthopyroxene, biotite and opaques. Kink bands, deformation twins, and core-mantle structures (fine-grained felspar rimming the older grain) in the the feldspars show evidence of strain accomodation. Aggregates of finer-grained serieate-lobate quartz grains with thickened grain boundaries and uniform extinction show evidence of grain boundary migration. Larger quartz grains with undulose extinction and deformation lamellae also indicate strain accomodation. The opaque mineral(s) have rounded, anhedral grain shapes and tend to cluster with biotite and orthopyroxene. Biotite is subhedral, with kink bands and undulose extinction; it is generally found in the intersticies between grains, most commonly adjacent to orthopyroxene grains. Orthopyroxene is subhedral and occasionally embayed. The other half of the thin section is dominated by two porphyroclasts of feldspar. This portion of the thin section abounds with symplectic intergrowths of quartz and feldspar as well as much subgrain development in both mineral. Growing normal to the rims of opaques and biotite grains is a poplulation of acicular aluminosilicate.

  • 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 BB19
    BB19

    This hypocrystalline thin section contains a trachytic groundmass of plagioclase laths, biotite needles, elongate strings of quartz, and serpentine pseudomorphs. The phenocrystic population consists of rounded quartz grains, often with a calcite rim, and concentrically-zoned, euhedral to subhedral plagioclase blocks. The plagioclase is being replaced in places by calcite, which is also found in fractures within the sample.

  • 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 BB22
    BB22

    The micas in this hypocrystalline rhyolite form euhedral needles and are generally aligned. Phenocrysts of plagioclase have been replaced by calcite and chalcedony. The groundmass of glass contains indiscernible crystals. This thin section is strongly altered and due to the fine grain size, difficult to identify minerals in.

  • 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 ERD1A
    ERD1A

    This coarse-grained dacite has a granitic texture of hypidiomorphic inequigranular plagioclase, hornblende, and augite. Secondary zeolites and calcite are found randomly throughout. This thin section is both too thick and plucking is disruptive of many hornblende grains.

  • Thumbnail for SG1A
    SG1A

    Plagioclase laths of varying sizes and orientations represent the bulk of this thin section. Augite is present, though in noticeably smaller quantities and olivine only in trace amounts. Tiny opaques pervade the sample.

  • Thumbnail for SS-6
    SS-6

    Most noteworthy in this sample are the millimeter-scale, euhedral, augite crystals with compositional zoning, twinning, more magnesian rims. Biotite is the subhedral phenocrystic phase in this sample and both are surrounded by interstitial nephaline. Several nephaline grains display micrographic-like intergrowths with a cloudy, difficult to identify phase. Equant olivine grains are frequently found as inclusions within pyroxene and biotite phenocrysts. Euhedral apatite are found throughout.

  • Thumbnail for CM2A
    CM2A

    Augite and olivine are the two predominant crystalline phases in this vesicular basalt and define a microporphyritic fabric. Iddingsite replacement of olivine is minimal. As smaller crystals, both phases, along with opaques, a feldspar, and glass, comprise the groundmass.

  • Thumbnail for PS-2d-troc
    PS-2d-troc

    Allotriomorphic plagioclase and highly-fractured olivine are the dominant minerals in this thin section. Clinopyroxene, when present, is found adjacent to olivine. Fractured zones in this rock follow olivine clusters and frequently cross-cut plagioclase crystals in swarms between nodes of granular olivine.

  • Thumbnail for BB13
    BB13

    In thin section, this flow-banded aphanitic rock displays a few fractured and embayed plagioclase and clinopyroxene phenocrysts in a groundmass dominated by aligned microlites of the same two phases. One or two phenocrysts of orthoclase are also present. The microlites define a trachytic texture, which is observable in handsample as flow bands.

  • Thumbnail for KBR12
    KBR12

    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.' If so, textures in this sample, though difficult to describe, better resemble those of igneous than sedimentary rocks. This sample is jumbled mess of bladed, graphically intergrown k-feldspar and clinopyroxene, subhedral plagioclase altering to a dendritic, cloudy mineral, patches of anhedral, granular quartz, and elongate, poikilitic opaques.

  • Thumbnail for KBR9
    KBR9

    Plagioclase and clinopyroxene form subhedral and anhedral grains, respectively, though unlike the other ferrotholeiites in this suite, both are cross-cut by or being pseudomorphed by iddingsite, a very dominant mineral in this thin section. Interstitial, undeformed quartz is found in the groundmass and inclusions of apatite crystals lend an almost graphic texture to this phase. Described by Western Minerals Inc. as an 'interstitial ferrotholeiite, very highly fractionated…textures are similar to those associated with rapidly frozen or highly viscous melts.'

  • 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 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 SC-22
    SC-22

    The plagioclase laths in this microporphyritic basalt are separated by size into seperate groundmass and phenocryst populations. Glass and opaques are the other groundmass phases. Clinopyroxene and its periodic pseudomorph calcite are additional phenocrysts.

  • Thumbnail for JPN-1
    JPN-1

    The phenocrysts in this basalt are plagioclase, orthopyroxene and clinopyroxene. Most pyroxenes are gathered in glomeroporphyroclasts with plagioclase, though the latter phase is most commonly found as isolated, irregularly twinned and shaped phenocrysts. The groundmass is glass and plagioclase.

  • Thumbnail for JPN-12
    JPN-12

    This cryptocrystalline basalt consists of a groundmass of plagioclase microlites, equant opaques, glass, and interstitial, anhedral phlogopite. Microphenocrysts of subhedral clinopyroxene comprise the remainder of the sample.

  • 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 JPN-22
    JPN-22

    This thin section is a jumbled mess of serpentine, chlorite, calcite, quartz, and other unidentifiable minerals. Texturally, it looks reminiscent of a basalt.

  • Thumbnail for J-26-11C
    J-26-11C

    This strongly foliated sample contains mostly hornblende crystals, the alignement of which defines the schistoscity. A granoblastic texture consisting of quartz, and highly poikiolblastic k-feldspar is interspersed among the hornblende grains. Occasional subhedral epidote and calcite grains crop up through the thin section. Of special note are a series of fractures that obliquely cross-cut the foliation; cataclastic textures can be observed along these zones. Small, rounded, colorless to light brown titanite crystals are present.