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53 hits

  • Thumbnail for JPN-19
    JPN-19

    Most of this thin section is serpentine. Scattered throughout are optically-continuous, serpentine-framed fragments of olivine and somewhat larger, texturally-similar orthopyroxene fragments.

  • Thumbnail for BATUR 1918
    BATUR 1918

    Subhedral phenocrysts of plagioclase, clinopyroxene, and olivine are scattered randomly throughout this basalt. Plagioclase has a sieve texture and is frequently zoned. The corners of most grains are rounded. Both clinopyroxene and olivine are generally equant in shape and olivine is more abundant than the pyroxene. All three phases show some degree of resorption. The groundmass contains moderately-sized crystals of all three phases. This sample is very fresh and unaltered.

  • Thumbnail for PS-1b-bs
    PS-1b-bs

    The groundmass of this basalt is composed of plagioclase microlites with tiny interstitial clinopyroxenes. Vesicles are infilled with chlorite and quartz. The few larger plagioclase phenocrysts have been partially altered to calcite.

  • 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 ERD9
    ERD9

    Two minerals, olivine and augite, comprise the phenocrystic population. Olivine is larger and more abundant. Both are present in the glassy groundmass, along with trace plagioclase laths, and abundant opaques.

  • Thumbnail for JPN-15
    JPN-15

    This inequigranular mosaic of pyroxenes and olivine is highly fractured. Subparallel swarms of high-density fractures are visible throughout and contain the highest concentrations of serpentine. The infilled minerals of one conspicuous vein have a nice comb texture.

  • Thumbnail for 59-K-91
    59-K-91

    This vesicular basalt contains microphenocrysts of olivine and orthopyroxene, both of which are also lesser components of the groundmass which consists mainly of uniformly-sized plagioclase laths. The olivine phenocryst have weak reaction rims. Some plagioclase is zoned and sieved.

  • Thumbnail for JPN-14
    JPN-14

    Texturally, this thin section still resembles a gabbro, with the exception of several talc and serpentine filled veins cross cutting the otherwise equigranular mosaic of clinopyroxene and olivine.

  • Thumbnail for SS-3674-6
    SS-3674-6

    This porphyritic sample contains phenocrysts of augite, olivine, and pseudoleucite. Olivine has an iddingsite rim when in contact with the groundmass. The pseudoleucite phenocrysts are a colorless and cloudy, roundish eight-sided crystals with first-order grey birefringence and extinction occurs in amoeboid-shaped sections within the phenocryst. These same pseudoleucite crystals make up the majority of the groundmass, along with calcite, k-feldspar and other alteration products. Three copies of this thin section contain the contact zone itself, with a calcite and clay-rich, layered Eagle sandstone.

  • 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 Bm
    Bm

    The outer rim of this bomb is glassy with vesicles and augite and olivine phenocrysts. Small, widely dispersed plagioclase microlites are also present. The core of the bomb contains a porous aggregate of fragmental quartz held together by glass.

  • Thumbnail for B2
    B2

    The outer rim phenocrysts of augite and olivine, though the red stain, which concentrates in the glass and olivine phases, obscures the characteristic birefringence of the olivine. Plagioclase microlites are present in the glass and calcite has infilled some pore spaces. The core of this bomb appears to be hematite and glass cemented tiny quartz crystals.

  • Thumbnail for CM4
    CM4

    The vesicles in this microporphyritic vesicular basalt are substantially smaller than the other Carr Mountain samples, though composition remains similar. More calcite permeates the groundmass, in which plagioclase microlites are visible. Unaltered augite and olivine microphenocrysts are observed. An isotropic zeolite, presumably analcite, is seen infilling several vesicles.

  • Thumbnail for JPN-13
    JPN-13

    As is characteristic of a harzburgite, this sample is greater than 90% olivine, with a few large clinopyroxene grains, fracture-infilled serpentine, and occasional, moderately-sized rutile grains making up the remaining constituents of the rock. Serpentinization is minimal.

  • Thumbnail for CF1A
    CF1A

    The olivine phenocrysts in this vesicular basalt are unaltered, in contrast to the second phenocrystic phase, plagioclase, which has a speckled, mottled alteration texture encroaching concentrically inwards from the grain boundaries. Only the cores and a thin corona of plagioclase on the outermost edges of the phenocrysts remains unaltered by this opaque phase. The glassy groundmass contains of unoriented plagioclase microlites and tiny olivine crystals. Olivine phenocrysts are larger and more abundant in CF1A than CF1B. The plucking in this sample is extensive, thus olivine phenocrysts are quite incomplete.

  • 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 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 SG2A
    SG2A

    Plagioclase microlites and small rounded crystals of augite and olivine define this thin section. The interstices between crystals are filled with reddish-brown glass.

  • Thumbnail for PS-3c-dun
    PS-3c-dun

    Strongly serpentinized dunite. Only 5-10% olivine remains. The characteristic serpentine mesh-work texture is highly evident in this thin section.

  • 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 484
    484

    Perthitic intergrowths of k-feldspar and albite are prevalent throughout this coarse-grained, nearly allotriomorphic granite. Riebeckite and biotite are found intergrown together in anhedral masses. The rare tiny, equant olivine crystal is observable.

  • 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-13
    SS-13

    This porphyroclastic thin section has a groundmass dominated by k-feldspar and zeolites, though other phases may be present in lesser amounts. The phenocrysts are euhedral augite and olivine, which are frequently found clustered together in glomeroporphyroclasts. The olivine is consistently rimmed by iddingsite and the augite frequently displays concentric zoning. Tiny crystals of equant apatite and rounded opaques thoroughly pepper the thin section.

  • 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 JPN-20
    JPN-20

    Interpenetrating zones of optically-continuous, pebbly-textured olivine, fibrous serpentine, and radiating talc. This thin section has interfingered scaly and fibrous textures.