Tourmaline was synthesized by heating the component oxides with water to 400-450 degrees C in a high pressure autoclave. The degree of filling was 60-70 percent at room temperature. The limits of stability of tourmaline at 400-450 degrees C as functions of the concentration of Na 2 O and B 2 O 2 were determined. It is concluded that tourmaline is stable in water solutions which have a low alkalinity and low to high solute concentration, but it is unstable in strongly acid and strongly alkaline solutions. Albite was found to be stable along with tourmaline in alkaline solutions containing less than approximately 45 percent of water.

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