Radiation-Induced Luminescence Color Images from Some Feldspars

Colorful luminescence images were obtained from some feldspar slices after X-ray irradiation. According to a ternary diagram of feldspars, afterglow color images (AGCI) were generously distinguished into two groups, giving intensely bluish or green coloration along the alkali feldspar (Or-Ab) line and weak reddish coloration along the plagioclase (An-Ab) line. In the former feldspar group, blue AGCI samples can be attributed to ordered crystals formed at a relatively slow cooling rate, whereas reddish AGCIs could be assigned to disordered crystals, presumably reflecting a rapid cooling process at formation or thermal alteration. In a microcline, alternative patterns of AGCI are closely related to a perthite structures, consisting of matrix microcline parts and stripe albite phases. Thermoluminescence color image (TLCI) patterns showed blue coloration similar to AGCIs in alkaline feldspars. Among the present feldspars, no homogeneously distributed luminescence existed. On the basis of the present results, the necessity for a single aliquot technique is emphasized for luminescence dating using feldspars.