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151 hits

  • Thumbnail for 990
    990

    The minerals in this sample all appear to intergrow with one another. Most grain boundaries are lobate, especially between feldspar phases and flame lamellae and perthitic intergrowths abound. Although a few hornblende crystals are euhdral in shape, the majority are found as rims around possible clinopyroxene or olivine grains and they tend to group with the other mafic phases. Euhedral apatite appear throughout.

  • Thumbnail for 867
    867

    This mineral phases in this gabbro are highly fractured and frequently embayed. The pyroxenes are roughly euhedral in shape and several equant grains are twinned. The opaques in this sample are typically equant in shape and contain inclusions of olivine or a fiery orange-red mineral that appears the same in plane- and cross-polarized light.

  • Thumbnail for 866
    866

    The feldspars in this granite are altering to clays and thus have a consistantly cloudy appearance. The indented grain boundaries in this sample indicate the mutual interference of all phases during growth. The anhedral shape of muscovite grains indicates it grew in the interstices between grains.

  • Thumbnail for 23-5A
    23-5A

    A continuous foliation defined by aligned euhedral biotite characterizes this fine-grained sample. Granoblastic quartz and feldspars fill the voids between biotite crystals. Small, equant opaqes are distributed evenly throughout.

  • Thumbnail for ERB-0X3
    ERB-0X3

    In this sample, a spaced, anastamosing schistoscity defined by biotite, garnet, hornblende and opaques wraps around deformed feldspar lenses which display undulose extinction and bent growth as well as deformation twins. Polyganized quartz and feldspar mantles the feldspar porphyroclasts. Quartz ribbons are prevalent throughout this sample. The sense of shear is ambiguous.

  • 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-3674-5
    SS-3674-5

    This is a very hypidiomorphic coarse-grained sample consisting of large grains of augite, frequently intergrown with opaques, and intergrown k-feldspar and nephaline. Augite is found altering to biotite. Radiating splays of zeolite are present to varying degrees within the three copies of this thin section.

  • Thumbnail for BB3
    BB3

    Large, euhedral to subhedral plagioclase blocks are in far greater abundance than either k-feldspar or quartz, both of which are anhedral in shape. All the ferromagnesian phases are anhedral in shape and tend to cluster together. Hornblende growth is at the expense of clinopyroxene. Opaques cluster with the ferromagnesian phases. Quartz displays first-order yellows in this slightly thickened sample.

  • Thumbnail for 504; 505
    504; 505

    The feldspars in this thin section are partially sericitized and somewhat poikilitic and the biotite is substantially altered. Grains are generally anhedral in shape.

  • Thumbnail for A-6-7
    A-6-7

    A continuous foliation for this sample is defined by aligned hornblende, micas, elongate quartz grains and granular aggregates of epidote and clinozoisite. Quartz is either equant or elongate with a granular texture. The hornblende phase is generally subhedral in shape, as are biotite crystals, which appear to be pseudomorphing an earlier mineral phase as evidenced by abundant inclusions. Radiation halos can be found in this sample though their occurrance is rare.

  • 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 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 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 Bs
    Bs

    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 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 SC-15
    SC-15

    This fine-grained, hypidiomorphic, inequigranular plutonic rock is intermediate in composition, with plagioclase as the dominant feldspar. K-feldspar is present in much lower abundance, and quartz is scarce. Mafic phases include anhedral biotite and hornblende, the latter of which is strongly chloritized.

  • Thumbnail for KBR7
    KBR7

    Plagioclase and clinopyroxene form subhedral, unaltered grains amongst a background of finer-grained, intermingled iddingsite and zeolites. 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 KBR4
    KBR4

    Plagioclase and clinopyroxene abundances are lower in this gabbro compared to others of Birds River. Radiating splays of zeolites with serpentinized margins, as well as iddingsite and chlorite replacement of an equant mineral phase contributes nearly half the bulk of the thin section.

  • 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 KBR3
    KBR3

    The clinopyroxene abundance in this thin section is lower than other gabbros from Birds River, lending more of a subophitic texture to the rock. Plagioclase is the most dominant mineral. Iddingsite is less abundant.

  • Thumbnail for JPN-18
    JPN-18

    The largest crystals in this sample, visible in handsample, are clinopyroxene, much of which has strong exsolution lamellae. Much smaller are the olivine crystals, which have subsequently been broken into a serpentine-framed mosaic of optically-continuous fragments.

  • 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 KBR10
    KBR10

    The unknown mineral is the prominent mineral in this thin section. It forms a dusty brown, isotropic matrix with a faint dendritic texture in which subhedral clinopyroxene and plagioclase grains are set. Clinopyroxene, where isolated, is strongly altered to iddingsite. The degree of alteration is much lower where plagioclase and clinopyroxene grains are intergrown. The two minerals have an almost graphic intergrowth texture. 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 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 SC-5
    SC-5

    There is no glass in this fine-grained thin section. Rather, allotriomorphic, randomly-oriented plagioclase is peppered with fine-grained granules of clinopyroxene and opaques. Few clinopyroxene phenocrysts cluster together to form glomeroporphyroclasts. The feldspars show signs of kaolinitization and sericitization.