Sample SP42 Quartz Monzonite Porphyry

Thin-Section Description

Quartz Monzonite Porphyry. This sample is a mildly altered holocrystalline, porphyritic-aphanitic, with fine- to medium-grained subhedral phenocrysts in a grey groundmass (8.7%) composed of fine-grained mica and feldspar. Minor amounts of quartz (1-2 mm) and carbonate (<1 mm) are present as anhedral crystals, while the following phenocryst phases are all subhedral: sieve textured plagioclase (1-3 mm) and potassium feldspar (1-3 mm) occur with the larger grains altering to fine-grained phyllosilicates; red biotite (1-5 mm) with inclusions of apatite; apatite (<.1 mm); chlorite (<1 mm). Overall texture is intergranular. Areas (1 mm2) are altered to fine-grained mica.