Minerals plagioclase

Musacchio et al. 1997 Novak et al. 1997 Chevrot van der Hilst 2000). Fp/Fs ratios are not sensitive to pressure and subsolidus temperatures, but depend on fluid pore pressure, fabric attitude and rock composition, specifically quartz content and plagioclase composition (Christensen 1996). In stable shield areas, high Fp/Fs ratios in the crystalline crust are generally explained in terms of composition. Mafic rocks have Fp/Fs ratios higher than 1.73 as a result of low quartz content and the abundance of mafic minerals (plagioclase, pyroxene, garnet, amphi-bole and olivine). 

Mantle rocks may be classified into those which are relatively enriched in the elements Ca, Al, Ti, and Na and those which are not. Lherzolites are "enriched" peridotites and are thought to be mantle rocks which have not melted and are known as "fertile" mantle -mantle from which a basaltic melt has not been extracted. Typically they contain a few percent of clinopyroxene and an aluminum-rich mineral (plagioclase, spinel, or garnet) in addition to the statutory olivine and orthopyroxene. Mantle which has experienced melt extraction is known as "depleted" mantle and has lower concentrations of the elements Ca, Al, Ti, and Na. This type of mantle is represented by the rock types harzburgite (peridotite without clinopyroxene and an aluminous mineral) and dunite. The relationship between a fertile mantle Iherzolite, depleted mantle harzburgite/ dunite and a basaltic melt is... 

Silicate minerals (plagioclase, almandine, biotite) Various soils 37-160 mm ka-1 Velbel (1986)... 

Most zeolites in sedimentary rocks formed during diagenesis by the reaction of aluminosilicate materials with the pore water. Silicic volcanic glass is the aluminosilicate material that most commonly served as a precursor for the zeolites, although materials such as clay minerals, plagioclase, leucite, and nepheline also have reacted locally to form zeolites (48). Solution of silicic glass by the pore water provided the constituents necessary for the formation of the zeolites. Deffeyes... 

Basalt fiber is composed of the minerals plagioclase, pyroxene, and olivine. It is similar to CF and glass fiber, having better physicomechanical properties than fiberglass, but is significantly cheaper than CF, as listed in Table 2.72 [74]. 

Clayton, J. L. (1986). An estimate of plagioclase weathering rate in the Idaho batholith based upon geochemical transport rates. In "Rates of Chemical Weathering of Rocks and Minerals" (S. M. Coleman and D. P. Dethier, eds). Chap. 19, pp. 453-466. Academic Press, New York. 

In zone (1), quartz, K-feldspar, epidote, chlorite, prehnite and sphene are predominant alteration minerals. Epidote, prehnite and carbonate replace plagioclase phenocryst. Epidote often occurs as a veinlet with several millimeters wide, together with prehnite. K-feldspar, calcite and quartz tend to occur as a veinlet. Chlorite replaces pyroxene... 

Hydrothermal alteration minerals from midoceanic basalt are analcite, stilbite, heulandite, natrolite-mesolite-scolecite series, chlorite and smectite for zeolite facies, prehnite, chlorite, calcite and epidote for prehnite-pumpellyite facies, albite, actinolite, chlorite, epidote, quartz, sphene, hornblende, tremolite, talc, magnetite, and nontronite for green schist facies, hornblende, plagioclase, actinolite, leucoxene, quartz, chlorite, apatite, biotite, epidote, magnetite and sphene for amphibolite facies (Humphris and Thompson, 1978). 

Among the minerals mentioned above calcite and kaolinite may be important for controlling /CO2 of terrestrial geothermal waters. It was cited by Giggenbach (1981) that /CO2 (or Xco2> mole fraction of CO2) of terrestrial geothermal waters is controlled by plagioclase -1- CO2 = calcite -H kaolinite . 

Figure 4. Fits of lattice strain model to experimental mineral-melt partition coefficients for (a) plagioclase (run 90-6 of Blundy and Wood 1994) and (b) elinopyroxene (ran DC23 of Blundy and Dalton 2000). Different valence cations, entering the large cation site of each mineral, are denoted by different symbols. The curves are non-linear least squares fits of Equation (1) to the data for each valence. Errors bars, when larger than symbol, are 1 s.d. Ionic radii in Vlll-fold coordination are taken from Shannon (1976).

Schaeffer et al. (1993) analyzed mineral phases extracted from the 1985 dacitic pumice erupted by Nevado del Ruiz (Colombia) pyroxene, plagioclase, magnetite, glass and whole rock define an U-Th isochron with a near-zero age (7 6 ka, 2g Fig. 10b). 

Many minerals are solid solutions (e.g., clays, amphiboles, and plagioclase feldspars). Solid-solution models are either not available or appropriate algorithms have not been incorporated into computer codes. 

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