Trace Element Characteristics, Luminescence Properties and Real Structure of Quartz

Abstract

Recent results on the cathodoluminescence (CL) and the trace element composition of quartz are the starting point to review the properties of quartz from different origin. CL-spectroscopy revealed five emission bands to be important in quartz additionally to one at approx. 340 nm which has been reported in the literature: the first one in the near-UV at 395 nm, the second in the blue range of the spectrum at 450 nm, the third at 505 nm (greenish blue), the forth at 570 nm (greenish yellow) and the last one in the red range of the spectrum at 650 nm. The bands at 395 and 505 nm are characterised by a strong decrease of intensities during irradiation while the band at 650 nm increases with increasing dose. This phenomenon is very common in quartz grown from aqueous solutions while magmatic quartz may show more stable luminescence emission. Trace element analyses display also differences in the composition between these two groups of quartz. Aluminium, Li and H have been found to be most important in authigenic, hydrothermal and metamorphic quartz but magmatic quartz is generally enriched in Ti. Germanium, Fe, B and Na is present at low levels in all quartz samples. A strong linear correlation between Al and Li indicates combined incorporation in [AlO4|Li+]-defects. A high unstable intensity at 395 nm has been observed especially in Al-rich quartz. In these samples, the luminescence commonly attenuates completely. However, different quartz samples show different correlation with Al. This result puts doubt on the interpretation that Al-related centres are the only reason for the near-UV emission. The emission band at 505 nm which also shows unstable behaviour in pegmatitic and hydrothermal quartz might also be related to trace elements, but the correlation is not well established. The increasing emission at 650 nm might be influenced by the water content of quartz, but the indicators for this interpretation are even more ambiguous than in the case of the 395 nm-band because SiOH-centres are commonly only present at very low levels. The emission bands at 450 nm, 505 nm (at least partly) and 570 nm are probably of intrinsic origin.