Sample SP58 Alkali-feldspar Syenite Porphyry

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Alkali-feldspar Syenite Porphyry. This rock is hypocrystalline, hypidiomorphic, porphyritic-aphanitic with subhedral phenocrysts in a grey-brown groundmass (13%) composed of potassium feldspar, clinopyroxene and minor amounts of glass. All crystals are subhedral except analcite (< 1 mm), olivine (<1 mm), and opaque minerals (<1 mm) which are subhedral to anhedral. Fluorite (<1 mm) and epidote (<1 mm) are present as anhedral masses. The following are present as phenocryst phases: Green hornblende (2-4 mm) exhibits contact twins and coronas; orthopyroxene and zoned titanaugite (1-2 mm); plagioclase and potassium feldspars (2-5 mm) are moderately, to completely, altered to fine-grained phyllosilicates; biotite (<1 mm) crystals are located around the edges of the hornblende; zircon and apatite (<.1 mm) are present with the latter found mostly as inclusions in hornblende. This rock also contains mafic enclaves (1-3 mm) composed of orthopyroxene, hornblende, opaques, apatite and fluorite (all .1-.5 mm). Fluorite is an alteration product associated with hornblende. There are also a few amygdules (.5 mm) rimmed by very fine-grained clinopyroxene with quartz cores.