ABSTRACT In the present work, we have used near infrared absorption in the region 3100-3700 cm -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+ centers in all samples of natural quartz suggests that the Al-OH- centers in these crystals become stable only after a certain maximum Al-Li+ 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.
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