Studies of colored varieties of Brazilian quartz produced by gamma radiation

Quartz occurs in Brazil mainly in two geological environments, called pegmatitic and hydrothermal. The quartz of hydrothermal origin occurs mainly in geodes in the basaltic rocks of the Parana Basin and the quartz formed in fracture systems of the Espinhaço Range. Quartz of pegmatitic origin forms often the core of pegmatites. The detailed mechanism of color center formation of these two types of quartz will be investigated by spectroscopic and chemical analysis. Until yet, it can be shown that due to chemical differences of the nature of mineral forming fluids, the two types behave differently. All quartz contains mainly traces of iron, aluminum, lithium and some amounts of water. The quartz of hydrothermal origin incorporated much structurally bound water, and despite some similarities with the chemical composition of pegmatitic quartz, this high water content is the reason for the formation of silanol radicals, giving green color to the quartz. The main difference in chemical composition of pegmatitic quartz is the presence of higher amounts of Al and Li, responsible for the brownish and yellowish colors formed by irradiation.