Plagioclase kaolinitized

Change kaolinite back into plagioclase Kaolinite... 

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 . 

CaAI2Si2Os (plagioclase) + H+ + HCO3 + H20 =CaC03 (calcite) +AI2Si205(0H)4 (kaolinite)... 

Figure 1. Logarithm of the ratio of Na+ to H+ in Sierra spring waters vs. logarithm of silica content. Solid circles are based on water analyses dashed lines are theoretical compositions that should result from the attack of C02-bearing water on plagioclase to yield solution plus kaolinite...

It is immediately apparent that the constituents added by deeper circulation are different from those derived by initial attack in some important ways. The ratio of Si(>> to Na+ in the increment is nearly 1 to 1. Because weathering of plagioclase to kaolinite releases dissolved SiOj and Na+ in a ratio of 2 to 1 (see Table II) and plagioclase is the only reasonable source of Na+, a solid other than kaolinite is being produced. Table IV is an attempt to deduce the reactions that occur during deeper... 

The over-all picture of what happens to the soil waters, as illustrated by Tables II and IV, is that initially they rapidly attack the rocks, kaolinizing chiefly plagioclase plus biotite and K-spar. As they penetrate more deeply, the reaction rate slows down, and both kaolinite and mont-morillonite are weathering products. Also, an important part of the Ca2+ comes from solution of small amounts of carbonate minerals. 

X 10"4 equivalents per liter and corresponds to the destruction of about 3.5 X 10 4 moles of plagioclase, 0.2 X 10"4 moles of biotite, and about 0.2 X 10 4 moles of K-spar. The annual precipitation in this part of the Sierra averages about 100 cm./year. Therefore, the rate of chemical weathering is about 3.6 X 10"r moles/year/sq. cm. If the rock consists of one-third plagioclase by volume, the rock should be disintegrated to an average depth of one meter in about 9000 years, and the residue would be chiefly a rubble of quartz, K-feldspar, and kaolinite. 

Figure 2. pK for equilibrium between Ca-beidellite and kaolinite plotted as a function of Na content of Sierra Nevada spring waters. Arrow ABC is the path of water evolution calculated for the reaction from Na0 62Ca038 plagioclase to kaolinite in a closed system with an initial dissolved C02 of 0.0006 moles per liter. Arrow ABD is the expected path if evolution is also controlled by the two-phase equilibrium kaolinite-montmorillonite... 

Intact soil cores (6.7 cm i.d.) were taken with spilt spoon at depths of 1 to 2 meters from a field test site located approximately 50 km east of Cincinnati, Ohio. The soil in this interval consists mainly of quartz (60%) and clay minerals (35%) with minor amounts of plagioclase and potassium feldspar. The majority of clay is illite and smectite, with minor amount of kaolinite. Soil chemical properties were analyzed prior to, and after, electroosmosis, in order to evaluate the effects of electroosmosis on the distribution of elements within the soil column. Sampled cores were wrapped in aluminum foil and stored at 12°C until the EO cell was assembled. 

Quartz Plagioclase K-feldspar Kaolinite Elite Montmorillonite Chlorite ... 

Obviously, the dissolution of the elements leads to change in the crystal lattice and the mineral composition. This can well be seen during the acidic treatment of montmorillonite or bentonite for catalytic purposes (Section 2.1). The treatment is done using concentrated hydrochloric, sulfuric, or phosphoric acid. X-ray diffraction studies show that a commercially available montmorillonite has low montmorillonite content (53%). The other constituents are illite 10%, kaolinite 6%, quartz 10%, plagioclase 5%, gypsum 1%, anhydrite 4%, and amorphous 7%. 

D -0.05 Gray underclay Quartz, kaolinite mica-illite Plagioclase... 

D 2.26 Dark clay parting Quartz, kaolinite, mica-illite Pyrite, plagioclase... 

D 2.51 Dark gray clay Quartz, mica-illite, kaolinite Plagioclase... 

D 3.04 Concretion zone Siderite, dolomite, quartz Mica-illite, kaolinite, plagioclase... 

Following Martinelli et al. (1989), the mineralogical composition of the particulate material in Amazon River is dominated by quartz and plagioclases, with a minor amount of kaolinite and smectites. Sediment transported by the Solimoes tributaries also shows the presence of quartz, gibbsite and kaolinite. Vermiculite is detected in the Rio I a and Rio Madeira, and mica is represented in the Rio Negro. 

The amount of plagioclase (Na and Ca) and smectite-vermiculite clay minerals decreases downstream, to the benefit of quartz and kaolinite. 

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