Pegmatite veins and the surrounding rocks. V. Secondary recrystallization of aplite to form pegmatite.

A new mechanism of origin of pegmatite by a process of secondary recrystallization of associated aplite is presented. Secondary recrystallization, driven by the reduction of the total interfacial or grain boundary free energy of a system, involves the growth of relatively few primary grains of a stable matrix by consumption of surrounding grains. The observations of the phenomenon as reported by metallurgists are incorporated into a hypothesis to explain the origin of pegmatites physically and temporally associated with aplite. The applicability of the hypothesis is evaluated with reference to examples from Skjærhalden at Kirkoy, southeastern Norway (Vogt, 1931). It is concluded that the formation of these pegmatites and their association with aplite can best be explained by invoking the new hypothesis of formation by secondary recrystallization of the aplite.