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55 hits

  • 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 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 KBR15
    KBR15

    According to Western Minerals Inc., this sample is a 'contact rock from sediment immediately above dolerite,…rock with quartz 'spots'–probably inverted from tridymite spherulites–in a matrix of devitrified glass with mullite and cordierite.' Due to the fine-grained nature of the sample, it is difficult to distinguish individual mineral phases in the allotriomorphic, equigranular, microcrystalline groundmass. The only noteworthy features in this thin section are the spherical, slightly coarser grained nodules with orange-brown rims.

  • Thumbnail for SC-20
    SC-20

    The glassy groundmass contains small plagiocase and clinopyroxene crystals, both of which are found as microphenocrysts. Plagioclase grains are variable in size and subhedral in shape. Clinopyroxene phenocrysts are substaniatlly larger, often due to the formation of glomeroporphyroclasts.

  • 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 JPN-2
    JPN-2

    Phenocrystic phases in this thin section are subhedral plagioclase, clinopyroxene, and orthopyroxene, found both as isolated crystals and as glomeroporphyroclasts. Some plagioclase phenocrysts have inclusions of equant pyroxenes and blebs of glass. Glass and plagioclase comprise the vesicular groundmass.

  • 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 JPN-5
    JPN-5

    Based on grain size, two populations of pyroxenes and plagioclase exist in this sample; the first are the fine-grained, equant crystals of the glassy groundmass, and the second, the subhedral to anhedral phenocrysts visible in handsample. The inconsistently-shaped plagioclase grains are sometimes zoned and frequently contain inclusions of glass.

  • Thumbnail for SC-21
    SC-21

    This thin section is comprised entirely of glass and aligned plagioclase microlites. A few hematite nodules are found throughout. One weathered biotite phenocrysts can be seen.

  • Thumbnail for SC-7A-BL
    SC-7A-BL

    The groundmass of this porphyritic basalt is predominantly glass with less abundant plagioclase microlites. The most readily-identifiable mineral of the phenocryst population is plagioclase. Of greater abundance are euhedral, opaque pseudomorphs. Rare inclusions of pyroxene are observed within these opaques. Pockets of chalcedony disrupt the otherwise uniform groundmass.

  • Thumbnail for 58-K-91
    58-K-91

    Unoriented plagioclase laths and interstitial glass and clinopyroxene make up the groundmass of this vesicular basalt. Olivine and orthopyroxene microphenocrysts are scattered throughout.

  • Thumbnail for JPN-3
    JPN-3

    The olivine that is so conspicuous in the JPN-3 handsample is conspicuously absent in thin section and represented by a mere 1 or 2 grains. Rather, phenocrysts of plagioclase and pyroxenes dominate the phaneritic phases. Both phases are subhedral and the plagioclase in particular indicates several different generations of growth. Some plagioclase is concentrically zoned, though most grains contain alternating inclusion-rich and poor zones. Inclusions are of pyroxenes and glass blebs. The groundmass contains glass, plagioclase microlites, and tiny pyroxenes.

  • Thumbnail for JPN-7
    JPN-7

    Although labeled an andesite on the sample record sheet, the presence of olivine and absence of hydrous mafic phases in this thin section indicate it is more basaltic in composition. Texturally, it is characteristic of a basalt as well, with a glassy and plagioclase-rich groundmass and phenocrysts of plagioclase, both pyroxenes and olivine. All phenocrysts are subhedral and plagioclase contains inclusions of glass.

  • Thumbnail for BB14
    BB14

    Phenocrysts of resorbed plagioclase and k-feldspar give this otherwise glassy rock its porphyritic texture. A couple of resorbed pyroxene phenocrysts are present. Aligned needles of an opaque phase give the glassy groundmass a trachytic texture.

  • Thumbnail for CF1B
    CF1B

    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 smaller and less abundant in CF1B than CF1A. Plucking of olivine crystals is extensive.

  • Thumbnail for SC-19
    SC-19

    The grain size of plagioclase laths in this porphyritic basalt ranges continuously from the groundmass microlites to milimetric phenocrysts. Glass and sparse equant pyroxenes comprise the remainder of the groundmass. Clinopyroxene phenocrysts are patchy due to plucking.

  • Thumbnail for SC-5-BL
    SC-5-BL

    The groundmass of glass and plagioclase microlites is host to euhedral phenocrysts of three euhedral mineral phases, plagioclase, hornblende, and biotite.

  • Thumbnail for CM3
    CM3

    Augite and olivine are the two crystalline phases in this 'cloudy' vesicular basalt. Iddingsite replacement of olivine is almost comprehensive; commonly, iddingsite nodes are the only indication of olivine's presence. The groundmass is microcrystalline and altered enough as to be unidentifiable.

  • Thumbnail for CM-incl
    CM-incl

    The layering in this thin section is defined by an opaque phase. Vesicles are pervasive throughout the rock and due to their abundance, the phenocrysts of olivine, pyroxene and feldspar appear to float freely on the slide. Epidote crystals are found among the opaque layers. The rock has a overall cloudy appearance.

  • Thumbnail for B[m+s]
    B[m+s]

    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 KBR19
    KBR19

    Fragmental quartz chunks in glass with occasional glass-surrounded plagioclase clusters. Western Minerals Inc. indicates this sample has partially melted to glass with tridymite developed.

  • 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.