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115 hits

  • Thumbnail for ERB-09a
    ERB-09a

    Grain boundaries between the quartz and feldspar phases in this sample are consistently lobate, often with finer-grained subgrains rimming each crystal. Quartz in undulatory. The mica phases are subhedral and often resorbed, with kink bands causing undulose extinction along the length of the grain. Along one edge of the thin section is a seam dominated by clinozoisite. A hematite stain gives a dusty orange appearance to the feldspars and fractures within the sample contain higher concentrations of the phase.

  • 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 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 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 174
    174

    This coarse-grained sample is dominated by anhedral and undulatory quartz and feldspar grains. Subgrains are observed in both phases. The birefringence of both quartz and feldspar are somewhat higher than usual, with both phases exhibiting lower first-order yellows and oranges. An isolated occurance of riebeckite is found at the far edge of one thin section and displays excellent amphibole cleavage and characteristic blue to yellow-green pleochroism. The other copies have highly altered purple-blue pleochroic minerals with indistinct cleavage.

  • Thumbnail for BB31
    BB31

    This sample has a granitic texture and contains roughly equal amounts of both feldspar phases. The k-feldspars are more sericitized than the plagioclase grains, many of which are concentrically zoned. The hornblende grains are anhedral and a times, form almost granular aggregates of equant grains. Hornblende is altering to chlorite, which also interfingers with the relatively subhedral biotite phase. Apatite and epidote are present in trace amounts.

  • 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 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 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 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 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 JPN-21
    JPN-21

    According to the sample information sheet, JPN-21 is a crossite-epidote-amphibole-bearing blueschist. Though mineral identification is somewhat complicated by the fine-grained nature of this foliated green rock, the dominant minerals appear to be quartz, chlorite, and calcite or aragonite, all of which are elongated and strongly aligned.

  • Thumbnail for SYH-1F
    SYH-1F

    A contact between blueshist and an omphacite boudin is captured in this thin section. The blueschist side is strongly foliated due to aligned glaucophane with interspersed sphene and minor muscovite and chlorite. The contact itself is an aggregate of sphene with interstitial chlorite and clinozoisite. Omphacite is the dominant mineral on the other side of the contact, though some glaucophane, muscovite, sphene, and clinozoisite is present. Quartz rims surround reddish opaques.

  • 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 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 ERB-09b
    ERB-09b

    This metamorphosed granite has a weak spaced foliation defined by moderately aligned elongate minerals and slight compositional layering. The opaque phases are segregated into two discrete bands, along which, large quartz grains show a crystallographically preferred orientation, causing them to appear nearly isotropic. Alternatively, this nearly isotropic phase could be untwinned leucite, however, an the lack of twins and association with the remaining phases is unlikely. The chlorite and muscovite phases appear to be collectively pseudomorphing a preexisting phase, as evidenced by dark, elongate inclusions within the chlorite grains.

  • Thumbnail for 51
    51

    A very poorly sorted rock with variably sized and angular quartz and feldspar pieces (both plagioclase and orthoclase; some fresh, others sericitized) set in a finer-grained matrix of chlorite, sericite, carbonate, silky quartz, leucoxene, magnetite and pyrite. Matrix chlorite corrodes quartz grains marginally. A few microfragments of rock (quartzite, granite, gneiss) also are present. Accessory detritals include muscovite, sphene, tourmaline and epidote. Most of the quartz pieces are markedly undulatory. A very low degree of incipient metamorphism is indicated by abundant secondary epidote in the matrix which also locally contains minute platelets of stilpnomelane.

  • Thumbnail for 44-7303
    44-7303

    This coarse-grained samples is dominated by subhedral quartzofeldspathic phases. The feldspars are altering to clays and the quartz extinction is undulose. The biotite phase is altering to chlorite in some places and is generally subhedral in shape; kink bands are found in some grains. The hornblende crystals are subhedral and generally cluster with the biotite.

  • 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 44-4205 interference figures
    44-4205 interference figures

    Ward's samples with oriented crystals to aid in finding interference figures.

  • Thumbnail for 507
    507

    Most crystals in this thin section are highly embayed, including the distinctive riebeckite grains.

  • 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.