Gamma radiation of quartz from Entre Rios (SC) and Quaraí (RS)

Abstract

The availability of gamma ray irradiators in Brazil increased the possibilities of the treatment of gemstones for color enhancement. One of the minerals with very high potential for these treatments is the quartz, a very widespread mineral with many colored commercial varieties. There is a specific variety of quartz in nature, showing a green color that may be produced artificially, by gamma radiation (60Co). In Brazil, the widely scattered geode occurrence from Quaraí, at Brazil southernmost location up to Uberlandia, in Minas Gerais, is one of these events. Quartz from these occurrences have been formed by strong hydrothermal activities. Hence, many quartz crystals showed a very fast growth occurrence, facilitating the formation of consequent defects and the uptake of water under the form of micro inclusions, molecular water, silanol (Si-OH) and OH. In the present work, the material analyzed is from hydrothermal regimes located near the towns Entre Rios and Quaraí. To characterize these materials, analyses have been made by ICP, NAA, electron microscopy, water loss techniques plus UV-VIS and NIR-FTIR spectroscopic measurements. Silanol complexes have been found by radiation, due to gamma rays forming the color center NBOHC (Non-Bonding Oxygen Hole Center), showing absorption between 590 to 620 nm and leaving a transmission window at about 550nm, responsible for the green color. The spectroscopic water determination showed less molecular water (up to 2300 ppm, per weight), probably due to remaining silanol complexes. The water content, with up to 3200 ppm by weight, exceeds the amount of charge balancing cations (Fe, Al, Li).