Feldspars adularia

Model the dissolution of quartz and K-feldspar (adularia) over time. Are the parameters temperature and C02 partial pressure of any importance Within the key word RATES use the BASIC program from the data set PHREEQC.dat. The calculation is done with distilled water (pH = 7, pE = 12) as a batch reaction over a time span of 10 years in 100 time steps at a temperatures of 5 °C and of 25 °C and at C02 partial pressures of 0.035 Vol% (atmosphere) and of 0.7 Vol% (soil). Calculate also the kinetics of the dissolution with 0.035 Vol% C02 and 25 °C for a period of 10 minutes. 

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.

Table 5.62 Chemical analyses of some natural feldspars (Deer et al., 1983). (1) orthoclase (Mogok, Burma) (2) Adularia (St. Gottard, Switzerland) (3) anorthoclase inclusion in augite (Euganean Hills NE Italy) (4) sanidine from a nepheline-leucitite (5) albite from a pegmatite (6) anorthite from a calc-silicatic rock. ...

Note The data set WATEQ4F.dat uses the name adularia for K-feldspar. Use EQUILIBRIUM PHASES to fix the oxygen concentration to 21 Vol%. Enter quartz with 0 0 under the same key word. While the first zero limits the... 

Partially ordered K-feldspars (such as orthoclase, adularia, and intermediate microcline) characteristically exhibit a tweed pattern consisting... 

Stillings L. L., Brantley S. L., and Machesky M. (1995) Proton adsorption at an adularia feldspar surface. Geochim. Cosmochim. Acta S9(S), 1473-1482. 

Figure 5 Highly microporous aggregate of authigenic albite replacing a K-feldspar (evidenced by the adularia overgrowth, K). Frio Formation, Oligocene, South Texas. SEM image (source Milliken, 1989) (reproduced by permission of SEPM (Society for Sedimentary Geology) fromi. Sedim. Petrol, 1989, 59, 364).

Stillings LL, Brantley SL, Machesky ML (1995) Proton adsorption at the adularia feldspar surface. Geochim Cosmochim Acta 59 1473-1482... 

Adularia Low temperature Na-feldspar Anhydrite Calcite Chalcedony Mg-chlorite... 

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