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8 hits

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    877

    This generally allotriomprhic-equigranular thin section is thicker than standar thin sections, thus the quartz and some k-feldspar grains display first order red to pink colors. The riebeckite is nearly opaque in both plane and cross-polarized light.

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    484

    Perthitic intergrowths of k-feldspar and albite are prevalent throughout this coarse-grained, nearly allotriomorphic granite. Riebeckite and biotite are found intergrown together in anhedral masses. The rare tiny, equant olivine crystal is observable.

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    174

    This coarse-grained sample is dominated by anhedral and undulatory quartz and feldspar grains. Subgrains are observed in both phases. The birefringence of both quartz and feldspar are somewhat higher than usual, with both phases exhibiting lower first-order yellows and oranges. An isolated occurance of riebeckite is found at the far edge of one thin section and displays excellent amphibole cleavage and characteristic blue to yellow-green pleochroism. The other copies have highly altered purple-blue pleochroic minerals with indistinct cleavage.

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    507

    Most crystals in this thin section are highly embayed, including the distinctive riebeckite grains.

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    485

    The k-feldspars in this granite have prominent perthitic intergrowths, which overprint obvious tartan and Carlsbad twins. Feldspars growth is more euhedral than that of other phases, though grain boundaries between feldspars are rather sutured. Anhedral riebeckite and biotite have seive-like textures. Olivine, if present, is found in trace amounts.

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    876

    The riebeckite grains in this sample are embayed in a skeletal fashion, with embayments strongly controlled by the amphibole cleavage. The feldspars have classic albite and tartan twins in addition to patchy lamellae.

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    874

    This thin section is divided in half diagonally by texture and grain size. The fine-grained side consists of roughly equigranular quartz, microcline, albite, biotite, and riebeckite. More quartzofeldspathic-rich portions have sutured grain boundaries whereas in more mafic patches the grains are typically equant and subhedral. The mineral phases in the coarse-grained half of the thin section are the same though the grain size increases several fold and clear grain boundaries are rarer.

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    Riebeckite

    A large riebeckite grain dominates this thin section.