The Distribution of Hydrous Impurities in Quartz : The Role of Twinning

Abstract

Quartz crystals have been studied since ancient times by scientists and natural philosophers attempting to unlock the mysteries behind their aesthetic appearance and cryptic morphological properties. Previous studies have begun to identify controls on the abundance and distribution of hydrous impurities (AlOH, LiOH and HOH) within gemmy hydrothermal quartz crystals collected from veins in the Swiss Alps. These studies used high-resolution (200 μm2 scans) traverses across sawn and polished crystal wafers that reveal trends in impurity concentrations both parallel and perpendicular to the c-crystallographic axis, as well as within optical ‘sector zones’ that correspond to growth on distinct rhombohedral and prism faces. Subtle differences in crystal structure between growth faces appear to influence the respective growth rates of the faces, resulting in a positive correlation of impurity concentration with growth rate. The differences in crystal structure also likely influence rate of impurity mobility, which results in the observed abundance profiles within the sector zones. We explore the effect of twinning on the abundance of hydrous impurities within single crystals. We aim to develop a comprehensive understanding of impurity behavior within quartz crystals in order to use their abundances to elucidate thermal and compositional histories of fluids within metamorphic hydrothermal systems.