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17 hits

  • Thumbnail for LS-06
    LS-06

    Well-sorted, rounded, clast-supported quartz sandstone with aggregates of chert filling in pore spaces. Quartz is undulatory and has early subgrain wall development.

  • Thumbnail for 56
    56

    A very fine-grained brownish-gray aggregate of chalcedonic quartz, scattered specks and aggregates of slightly coarser quartz and irregular stringers and blebs of translucent to opaque organic material. Local patches and grains of fossiliferous calcite appear.

  • Thumbnail for LS-03
    LS-03

    Moderately sorted, subangular, matrix-supported, quartz and glauconite sandstone with calcite and hematite matrix. Quartz is undulatory with subgrain walls developing and potassium feldspar twins are deformed. Pockets of finer-grained material contain rounded epidote grains.

  • Thumbnail for LS-02b
    LS-02b

    The bulk of this sample is composed of microcrystalline limestone interspersed with calcite rhombs and transected by veinlets of clay and coarse-grained calcite.

  • Thumbnail for LS-01
    LS-01

    A moderately-sorted, subrounded quartz sandstone with a calcite cement. Microcline and albite are present in smaller amounts than the quartz clasts. A luster-mottling texture is present, in which the calcite cement forms crystals larger than the clasts it cements, as indicated by the optical continuity and parallel twins across large portions of the thin section's cement. Layering is observed in thin section by zones of abundant cement alternating with more clast-supported, calcite-poor zones. Most quartz clasts show undulatory extinction and subgrain development.

  • Thumbnail for 52
    52

    Microscopically mainly cryptocrystalline and merely translucent in shades of gray-brown. Subordinate silty quartz grains, feldspar pieces, sericite flakes, calcite rhombs, and a few particles of pyrite, zircon, magnetite and leucoxene. The dark matrix is composed mainly of illitic clay material.

  • Thumbnail for =56
    =56

    Fine-grained rounded aggregates of chalcedonic quartz set in a matrix of chalcedony and hematite. Veinlets of chalcedony hematite crosscut the sample.

  • Thumbnail for LS-07a
    LS-07a

    This well-sorted, subrounded, chert-cemented quartz sandstone contains alternating clay-rich and poor layers. Accessory minerals and microcrystalline calcite are concentrated along the clay or hematite-rich layers. Hematite concretions and veinlets are found in this sample.

  • Thumbnail for 51
    51

    A very poorly sorted rock with variably sized and angular quartz and feldspar pieces (both plagioclase and orthoclase; some fresh, others sericitized) set in a finer-grained matrix of chlorite, sericite, carbonate, silky quartz, leucoxene, magnetite and pyrite. Matrix chlorite corrodes quartz grains marginally. A few microfragments of rock (quartzite, granite, gneiss) also are present. Accessory detritals include muscovite, sphene, tourmaline and epidote. Most of the quartz pieces are markedly undulatory. A very low degree of incipient metamorphism is indicated by abundant secondary epidote in the matrix which also locally contains minute platelets of stilpnomelane.

  • Thumbnail for 60
    60

    Interlocking microcrystalline calcite crystals and microspar with veinlets of hematite. (Angular fragments of turbid, fine-grained, distinctly layered limestone are cemented and veined by clear, much coarser grained calcite. The limestone pieces contain uniformly fine-grained calcite, veinlets and patches of hematite, small aggregates of chalcedony, grains of sand and silt-sized quartz and disseminated shreds of opaque carbonaceous debris. Some pieces are so fine-grained that they approach the texture of lithographic limestone.)

  • Thumbnail for LS-05
    LS-05

    This porous, fine-grained, well-sorted, well-rounded, clast-supported quartz sandstone is cemented together with hematite. Clasts of microcline, hornblende, calcite, and chert are dispersed in minor amounts throughout the sample. The layering which is visible to the naked eye is unnoticeable in thin section.

  • Thumbnail for 57
    57

    Chalcedonic quartz forms pseudomorphs after carbonate oolites. Both concentric and radial internal structures are preserved. Where and oolite is sectioned centrally the sandgrain nucleus appears. Both the oolites and scattered quartz sand grains are set in a matrix of fine-grained chalcedony.

  • Thumbnail for 49
    49

    A uniformly fine-grained parallel-oriented aggregate of angular quartz grains, feldspar fragments, chlorite flakes, sericite flakes and shreds, aggregates of submicroscopic clay minerals (chiefly kaolinite), and carbonaceous shreds. Accessory detrital species recognizable are biotite, apatite, zircon, epidote, and tourmaline.

  • Thumbnail for LS-02a
    LS-02a

    The bulk of this sample is composed of microcrystalline limestone interspersed with calcite rhombs and transected by veinlets of clay and coarse-grained calcite. According to the collectors, this sample was collected because of its replacement textures.

  • Thumbnail for LS-04a
    LS-04a

    Poorly-sorted, angular, clast-supported, arkosic conglomerate with large clasts of deformed quartz and microcline. Many feldspar grains are altering to clays. Deformed micas are interspersed throughout. Perthite and scotch-plaid twins are extensive. The cement is comprised of microcrystalline quartz and locally, calcite.

  • Thumbnail for LS-04b
    LS-04b

    This moderately-sorted, clast-supported, angular, micaceous sandstone is cemented with microcrystalline quartz and localized calcite. A red hematite stain pervades the sample and concentrates along weathered feldspars. The elongate micas are warped and decaying.

  • Thumbnail for LS-07
    LS-07

    This micritic limestone contains lenticular, semi-spherical, and hexagonal fossils, all calcareous themselves.