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9 hits

  • Thumbnail for SS-3674-4
    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
    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-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 SS-3674-8
    SS-3674-8

    A few biotite phenocrysts punctuation this sample's fine-grained groundmass of unoriented elongate biotite, k-feldspar, nephaline crystals and anhedral calcite masses.

  • Thumbnail for SS-10
    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-4
    SS-4

    Randomly oriented biotite phenocrysts dominate this thin section. The interstices between phenocrysts contain prisms of k-feldspar, anhedral masses of calcite and nephaline, and radial splays of muscovite. Opaques are equant and up to 0.5mm in diameter. The nephaline phase has a bluish cast in cross-polarized light. The groundmass phases are cross-cut by a mesh-work of clays and various alteration products. Slightly diamond-shaped rutile is pervasive throughout.

  • 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 SS-3674-2
    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 SYH-1FF
    SYH-1FF

    This blueschist consists mostly of aligned glaucophane, micas, and sphene. Occasional inclusion-rich porphyroclasts of nephaline are observed.