REACTIONS OF FELDSPAR AND MICA WITH WATER AT LOW TEMPERATURE AND PRESSURE 1 by

Muscovite and K-feldspar (adularia) were dry-ground to-- 200/inch particles, which were suspended in water. These suspensions were " t itrated " with KC1, and the pH was recorded as a function of KC1 concentration and temperature. The results indicate that muscovite and adularia react with water to produce a surface film in which H+ has displaced I~+. The " titration " curves show some characteristics attr ibutable to exchange reactions, others apparently related to equilibria among solids of fixed com-position. ~V~aximum release of K+ from adularia by reaction with water is much greater than that from mica. The interpretation is made that the first result of reaction of mica and adularia with water is a surface layer that grades from an outer portlon that is structurally disrupted to an inner portion that retains the original silicate structure but with H + substituted for K+. Addition of K + as KC1 to the suspending solution displaces I-I ~ from the disrupted zone, but all I-I+ originally taken up by the solids was not returned to the solution by conceutratlons of KC1 up to 1.0 ~. Experiments were of a few hours duration; work by others has show ~ that the disrupted zone releases appreciable concentrations of silica and alumina to solution over longer t ime intervals. These hydrolysis experiments indicate that at 25 ~ an I-Lfeldspar or/-I-mica structure is favored over a K-feldspar or K-mica structure xcept in solutions in which the ratio of aK+ lag+ exceeds 109-1 ~ or 107-s respectively. These ratios decrease in the temperature range 25-65 ~ by a factor of about 10 ~ These results, where considered in relation ~o the observed behavior of feldspar and mica under weathering conditions, indicate that the major energy change for the reactions, 2 mica-~- 5H20 ~ 3 kaolin- ~ 2K + d- 2Ott-3 K-feldspar d- 2H~O ~ K-mica ~- 6 quartz d- 2OH-can be considered to result from H+-t ~ + exchange, and that the energy contribution from other changes is small