The major ions dissolved from 10-gram samples of 138 silicate rocks ground for 1 hour at room temperature under 100 ml distilled water exposed to the atmosphere were determined in the clear centrifugate from the grinding suspension. Mean values of dissolved ions from 41 quartz-phanerites are about 3 ppm Mg, 5 ppm Ca, 7.5 ppm Si, 17 ppm Na, 12 ppm K, and the pH of the rock slurries ranges from 8.2 to 9.2. Gabbro-diabase-basalt flow rocks yield mean concentrations at about 4 ppm Mg, 11 ppm Ca, 8 ppm Si, 14 ppm Na, 4-12 ppm K (low value from basalt), and the pH of these slurries averages slightly higher than that of granite slurries. The most reactive and soluble rock observed was orendite pumice, from the Leucite Hills of Wyoming, which yielded 32 ppm Si (or 68.6 ppm SiO 2 ), 0.3 ppm Al, 1.9 ppm Mg, 1.4 ppm Ca, 25.6 ppm Na, 130 ppm K, total dissolved ions 198 ppm, and pH 10.5 in the rock slurry. The solubility of Si is enhanced by dissolved Na and K, but reduced by dissolved Ca, Mg, and Al (conduces formation of secondary minerals). Dunite dissolved nearly stoichiometrically. The availability of nutrient ions (for plants) from native rocks as agstones is pointed out.

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