Abstract
The concentrations of aqueous solution from which quartz, feldspar, topaz, tourmaline and other minerals crystallize during the hydrothermal stage, is important to an understanding of pegmatite formation. Two opposing theories have been advanced on solution concentration: 1) Pegmatitic minerals separate from highly concentrated solution, without marked change in concentration, by gradual cooling. 2) Pegmatitic minerals separate as a result of flow and of renovation of the exhausted contents of solutions; this need is based on low solubility of silica in pure water. Study of liquid inclusions in minerals reveals that separation of hydrothermal minerals is known to occur from aqueous solutions heavily saturated with alkaline-halide salts, carbonates, borates, and free carbonic acid. From observations made on secondary liquid inclusions in topaz samples from pegmatites, it was found that one-third of the inclusion-cavity volume was occupied by the gas bubble and the remainder of the volume, largely, by small...
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