Sample SP33 - West Spanish Peak

Quartz Syenite

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40Ar/39Ar age spectra for SP33

Thin-Section Description

(West Spanish Peak). Quartz Syenite. This rock is holocrystalline, phaneritic, fine- to medium-grained, hypidiomorphic-granular. All phenocrysts are subhedral except for anhedral grains of quartz (1 to 3 mm) and the opaques (< 1 mm) which are subhedral to anhedral. The following are present as phenocryst phases: Plagioclase (1-5 mm) is moderately altered to fine-grained phyllosilicates with some grains exhibiting oscillatory zonation; orthoclase (.5-3 mm) exhibits undulatory extinction, moderate alteration, and some inclusions of apatite; diopside (.5-2 mm) is extensively altered to chlorite with inclusions of anhedral opaques (<.1 mm); biotite (.5-5 mm) grains contain (<.1 mm) opaques as inclusions; phlogopite (.5-2 mm) contains very fine-grained subhedral to euhedral inclusions of apatite; apatite (< 1 mm) is present as subhedral to euhedral crystals. Orthoclase was the phase dated.