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30 hits

  • Thumbnail for SS-3674-4

    The groundmass of this thin section comprises an intergrowth of k-feldspar and nephaline, as well as small euhedral diopsidic-augite crystals, biotite, and apatite. The phenocrystic phases are dominated by augite, many with partial rims of more diopsidic composition, and which are frequently zoned and twinned. Olivine is present adjacent to the pyroxenes and is commonly altered to biotite.

  • Thumbnail for SS-3674-3

    The largest crystals in this sample are augite, in which twinning is common, as is alteration to a mixture of chlorite and biotite, and the formation of glomeroporphyroclasts. Chlorite and biotite also are found rimming olivine grains, which are themselves clustered with augite and biotite crystals. The mafic phases are typically subhedral in shape, in contrast to the nephaline, k-feldspar, and zeolites which are anhedrally intergrown together in the interstices between augite crystals.

  • Thumbnail for SS-1

    The dominant mafic phase in this thin section is biotite, followed by augite. These two phases comprise the phenocryst population. Due to secondary alteration, the once euhedral grains of augite are now 'patchy' in appearance. The groundmass consists of a cloudy matrix of biotite microlites set amongst a indistinguishable mixture of sanidine and zeolites. Interstitial calcite is found in the groundmass, and can be seen infilling voids in the augite phenocrysts.

  • Thumbnail for 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 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 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 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 102

    This fine-grained dacite has a strongly cloudy appearance throughout, as well as a film on the surface of the slide that prevents clear focusing. Dusty plagioclase, plucked hornblende, and equant augite are the dominant phases. Euhedral apatite crosscuts most samples. Zeolites and calcite fill most voids or interstices.

  • Thumbnail for 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-3674-2

    The bulk of this thin section is augite. In plane polarized light, these grains have pleochroic rims of differing composition, which translates to concentric zoning in cross-polarized light. Twinning is common, as is alteration to a mixture of chlorite and biotite, and the formation of glomeroporphyroclasts. Chlorite and biotite also are found rimming olivine grains, which are themselves clustered with augite and biotite crystals. The mafic phases are typically subhedral in shape, in contrast to the nephaline, k-feldspar, and zeolites which are anhedrally intergrown together in the interstices between augite crystals.

  • Thumbnail for 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

    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 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 ERB-23

    Intergrown, subhedral two-pyroxene gabbro with hornblende and poikilitic plagiclase with deformation twins and abundant pyroxene inclusions.

  • Thumbnail for 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 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 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 ERD2

    This seems to be a porphyritic basalt though the phenocrystic phases, presumably augite, are plucked enough as to be virtually nonexistent. The remainder of the thin section is a glassy groundmass with unoriented microlites. The microlitic phases are probably pyroxenes and plagioclase, though color, relief, birefringence, and extinction angles seem incongruent with these minerals.

  • Thumbnail for 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 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 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 SS-10

    Phenocrysts in this thin section are of augite, biotite, and opaques. Uralitization of augite is observed in one region of the sample and is absent elsewhere. One augite crystal appears dendritically intergrown with opaques. Nephaline, which is the dominant groundmass mineral, appears intergrown with another mineral though it is unclear which. These intergrowths are spherical in shape and observable at the macroscopic scale. Prismatic and radiating fibers of zeolites are found throughout. Apatite crystals span a great range of sizes with the longest crystals reaching more than a millimeter in length. Apatite crystals of a smaller size pervade the nephaline phase.

  • Thumbnail for SS-3

    This coarse-grained sample contains phenocrysts of a wide variety of size and composition. The largest, visible in hand sample as whitish spheres with obvious rims, are intergrown, wedge-shaped k-feldspars and radiating blades of natrolite. A dusting of sericite throughout the k-feldspar gives a cloudy appearance to the these mineral aggregates. Randomly oriented grains of these same phases comprise the bulk of the 'groundmass' for this sample. Augite phenocrysts are the dominant mafic phase and display a variable degree of alteration to iddingsite?. A few grains of arfvedsonite can be seen associated with the pyroxenes.

  • Thumbnail for SS-2

    This hypocrystalline thin section contains euhedral to subhedral phenocrysts of augite and eight-sided, rounded, phenocrysts of a colorless, moderate-relief, very weakly birefringent mineral, perhaps leucite, sodalite, or analcite. The groundmass of indistinct, microlitic k-feldspar and pyroxene is rich with equant opaques and cloudy in appearance.

  • Thumbnail for SW9

    This coarse-grained sample consists of equant, subhedral bronizite crystals with few large, anhedral plagioclase and augite crystals filling the interstices between grains.