Clinopyroxene quartz

Newton R. C. and Perkins D. (1982). Thermodynamic calibration of geobarometers based on the assemblages garnet-plagioclase-orthopyroxene (clinopyroxene)-quartz. Amer. Mineral, 67 203-222. 

The rocks of the NS-N dyke group range from nepheline syenite to sodalite-bearing nephelinolite. The primary phases in the NS-N dyke group are k-feldspar and nepheline, with variable abundances of amphibole, plagioclase, phlogopite, calcite, sodalite, titanite, cancrinite, apatite, clinopyroxene, zircon, chlorite, quartz, pyrochlore, and opaque phases. 

Retrograde metamorphic processes, linked to hydrothermal fluid circulation, finally produced a new mineral assemblage constituted mainly by tremolite-actinolite> epidote + chlorite + quartz + sericite + titanite + hematite. The amphibole appears as green fibrous crystals over clinopyroxene and other anhydrous minerals. 

Figure 3.29 The low-pressure tholeiitic basalt phase diagram after Cox et al (1979). The inset shows that the projection is from normative quartz onto the critical plane of silica undersaturation modified to olivine-plagioclase-clinopyroxene in the Yoder—Tilley basalt tetrahedron.

The Plogen nunatak consists of about 30 basalt flows most of which are porphyritic with phenocrysts of plagioclase, ohvine, and pyroxene in a groundmass of plagioclase laths, clinopyroxene, Fe-Ti oxides, and mesostasis. The plagioclase phenocrysts of many flows are altered to sericite and, in some cases, have been converted to pseudomorphs of saussurite (mixture of alteration products containing chlorite, calcite, albite, and epidote). Olivine was also altered, but clinopyroxene is pristine, hi contrast to the pervasive alteration of the flows, the basalt dikes are unaltered. The flow tops are typically amygdaloidal and the former vesicles are filled with chlorite, quartz, prehnite, and calcite. 

Shock polymorphic transformation of qirartz into stishovite (swelling of quartz) local heating and pressure upon the accirmirlation of clinopyroxene expanding stishovite Partial disordering of clinopyroxerre allocation of sodinm and calcium —> allocation of carbon, vanadinm, sirlfur and other elements of the solid solution and the diffusion of chromium —> damage to the litre dust particle melt. 

Similarly, equilibrium between anorthite, quartz (both pure) and a clinopyroxene solid solution fixes at known pressure and temperature, the activity of CaAl SiOg component in the pyroxene ... 

The relationship between activity and mole fraction of the CaAl2Si0g component in clinopyroxenes has been studied by the author (see Wood, 1976 for a preliminary report) using a similar method to that just described for garnet solutions. If clino-pyroxene coexists with anorthite and quartz under equilibrium conditions at known P and T then a a 2Si06 defined by the relationship ... 

The compositions of clinopyroxenes coexisting with anorthite and quartz have been determined over a wide range of pressure and... 

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