Sweeping investigations on as grown Al-Li/sup +/ and Al-OH/sup -/ centers in natural crystalline quartz

In the present work, we have used near infrared absorption in the region 3100-3700 cm/sup -1/ to study a variety of optically clear samples of natural quartz crystals of Brazilian and Arkansas origins. The crystals used were hydrogen-rich and hydrogen-lean with approximately equal and also of varying aluminum concentrations. The alkali-H concentration in hydrogen-rich samples was much higher than that in the hydrogen-lean samples. The crystals were investigated in their as-received (unswept or Li-swept), Na- and H-swept conditions. The very narrow variation in the strength of grown-in Al-Li/sup +/ centers in all samples of natural quartz suggests that the Al-OH/sup -/ centers in these crystals become stable only after a certain maximum Al-Li/sup +/ concentration. This concentration appears to be independent of the origin of the growth and reflects a characteristic feature of the growth mechanism of natural quartz crystals.<>