Die mannigfachen Farben von Quarzkristallen gehen stets auf die Anwesenheit von Fremdatomen zuruck, deren Konzentration selten 0.1 Gew.-% iiberschreitet. Die Fremdatome besetzen entweder Gitterplatze des Siliciums oder Zwischengitterplatze in den Kanalen 11 c der Quarzstruktur : seltener lassen sich feinste Ausscheidungen fremder Phasen beobachten.AuRer Eigenfarbung von ifbergangsmetall-Ionen findet man Farbzentren, die durch ionisierende Strahlung entstehen. Wachstumsbedingt konnen sich im Kristall gesetzmLBige Verteilungen von Fremdatomen und Farbe ausbilden. In synthetischen Quarzen konnten die meisten der naturlichen und weitere in der Natur nicht auftretende Quarzfarben erzeugt werden.
Earlier observations on the deformation of rock-forming quartz during Alpine metamorphism that were made by Voll (1976) along a traverse following the reuss valley (Aar massif, central swiss Alps) are still relevant but can be explained in more modern term. Voll found that a few kilometres south of the contact between the Aar massif and its sedimentary cover quartz has partly undergone a combination of dynamic recrystallization and nucleation along grain boundaries and fractures at the expense of the deformed parent grains. Further to the south, increasing grain growth of quartz under nearly static conditions is observed, with polygonal grain shapes typical of annealed microfabrics. comparable stages of recrystallization could be found in several N-s traverses through the Aar massif so that "points of first occurrence" of newly formed quartz could be connected to define a quartz recrystallization isograd. this isograd extents over 90 km through the northern Aar massif, following a course parallel to the sanidine/microcline isograd but at a distance of 10-15 km further to the north. the evolution of the quartz microfabric is discussed with respect to recent estimates of the t-t path of the Aar massif.
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