It is present as a fine crystalline dispersion throughout the glassy phase that is produced by the melting of the feldspar. The feldspar fuses when it melts, forming a glass matrix. The feldspars are mixtures of potassium aluminosilie (K 2 O Al 2 O 3 6SiO 2) and sodium aluminosilie, also known as albite (Na 2 .
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