Minerals anorthite

This reaction is the source of H2 gas and OH (which is shown here as forming brucite) in the hydrothermal fluids. Peridotite is also composed of the mineral anorthite. As shown in Eq. 19 3, albitization of this mineral supplies Ca " to the hydrothermal fluids. This type of hydrothermal system is much more stable than the high-temperature ones... 

Definition Occurs in nature as the minerals anorthite, didymolite, lawsonite, etc. 

The two large groups of clays used in ceramics, kaolinite and montmorillonite, are both erosion products of weathered feldspar minerals. For example when the rocky mineral anorthite is eroded by weathering, kaolinite particles are formed ... 

Most igneous and metamorphic rocks are composed predominantly of alurninosiHcate minerals, including feldspar such as albite (NaAlSi Og) or anorthite (CaAl2Si20g) and crystalline forms of siHca such as quartz (Si02). Various mixed metal-plus-siHcon oxides such as oHvine [(Mg,Fe)2(SiO ] and... 

Figure 1.140. The dependence of concentration of K+, Na, Ca + and HaSiOa in equilibrium with common alteration minerals (K-feldspar, Na-feldspar, quartz) with temperature (Shikazono, 1988b). Thermochemical data used for the calculations are from Helgeson (1969). Calculation method is given in Shikazono (1978a). Chloride concentration in hydrothermal solution is assumed to be 1 mol/kg H2O. A-B Na+ concentration in solution in equilibrium with low albite and adularia. C-D K+ concentration in solution in equilibrium with low albite and adularia. E-F H4Si04 concentration in solution in equilibrium with quartz. G-H Ca " " concentration in solution in equilibrium with low albite and anorthite.

All of the Type A and B inclusions studied are surrounded by a layered rim sequence of complex mineralogy [21] which clearly defines the inclusion-matrix boundary. Secondary alteration phases (grossular and nepheline, especially) are also a common feature of these inclusions, suggesting that vapor phase reactions with a relatively cool nebula occurred after formation of inclusions. Anorthite, in particular, is usually one of the most heavily altered phases the relationship between Mg isotopic composition and alteration is discussed below. (See [12] for striking cathodoluminesce photographs of typical Allende alteration mineralogy.) Inclusion Al 3510 does not fit the normal pattern as it has no Wark-rim and does not contain the usual array of secondary minerals. 

Ca (aq), Mg (aq), and HCOjCaq). Silicate weathering is an incongruent process. The most important of these reactions involves the weathering of the feldspar minerals, ortho-clase, albite, and anorthite. The dissolved products are K (aq), Na (aq), and Ca (aq), and the solid products are the clay minerals, illite, kaolinite, and montmorillonite. The weathering of kaolinite to gibbsite and the partial dissolution of quartz and chert also produces some DSi,... 

Figure 11.30 Reduced partition function for various minerals calulated by Kieffer (1982) through equation 11.61 plotted against T. Heavy curve labeled H20(l) is reduced partition function of water according to Becker (1971). Dashed curve is a extrapolation of high-r reduced partition curve for quartz. Mineral abbreviations Qtz (quartz), Calc (calcite), Albt (albite), Muse (muscovite), Enst (clinoenstatite), Anor (anorthite). Diop (diopside), Pyrp (pyrope), Gros (grossular), Zron (zircon), Fors (forsterite), Andr (andra-dite), Rutl (rutile). Reprinted with permission from Kieffer (1982), Review of Geophysics and Space Physics, 20, 827-849, copyright 1982 by the American Geophysical Union.

Goldsmith J. R. (1980). The melting and breakdown reactions of anorthite at high pressures and temperatures. Amer Mineral, 66 1183-1188. 

Figure A4-1 Comparison of oxygen diffusivity in various minerals under hydrothermal conditions- Mineral names (from high to low diffusivity) An, anorthite Ah, albite Bt, biotite Ms, muscovite Phi, phlogopite Cc, calcite Qz, quartz Ap, apatite Mt, magnetite Hb, hornblende Tr, tremolitel Tt, titanite Di, diopside Rut, rutile Aim, almandine.

Elphick S.C., Graham C.M., and Dennis P.F. (1988) An ion microprobe study of anhydrous oxygen diffusion in anorthite a comparison with hydrothermal data and some geological implications. Contrib. Mineral. Petrol. 100, 490-495. 

Tsuchiyama A. (1985a) Dissolution kinetics of plagioclase in the melt system of diopside-albite-anorthite and origin of dusty plagioclase in andesites. Contrib. Mineral. Petrol. 89, 1-16. 

The mineral trapping takes place in three steps as demonstrated by the example of anorthite dissolution ... 

Feldspars may be refractory as well or crystallized from partial melts. Whereas potassium feldspars are found to be mostly refractory, anorthite rich plagioclase may be newly formed. Pyroxene and spinel were identified in varying amounts but no olivine could be detected. Metals and iron oxide minerals (magnetite-hematite) are always present in BA, but have not been quantified yet. In Table 4 the amount and the ranges of measured mineral contents are summarized. 

Figure 3.24. Morphodroms of silicate minerals [23]. (a) Summarized results on quenched samples anorthite (An)-albite (Ab) series, (b) Summarized observation obtained by in situ method diopside (Di)-anorthite (An) system.

CAIs are composed of a variety of minerals, primarily hibonite, perovskite, melilite, spinel, aluminum- and titanium-rich diopside, anorthite, forsterite, and occasionally corundum or grossite. They also show significant enrichments in refractory trace elements. CAIs exhibit a host of isotopic anomalies inherited from incorporated presolar grains or from the early nebula itself. 

On the other hand, fine-grained CAIs consist of aggregates of nodules with a concentric structure consisting of spinel cores surrounded by melilite, anorthite, and diopside, or melilite cores surrounded by anorthite and diopside (Fig. 7.5). The sequence of minerals in the nodules is consistent with a condensation sequence. However, the textures of the overall objects are complicated and often indicate extended and multistage histories. For... 

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