抄録
Labradorescence in the color zoning, in which remarkable change of lamellar thickness and An content are observed, is discussed. A wide-area macro-analysis in the region of color zoning is performed by using “X-ray contour mapping” with computer controlled electron probe microanalyzer, which has hitherto been infeasible with conventional automated electron probe microanalyzer.
The result of mapping analysis in a wide area agrees with the Bøggild rule between An content and interference color reported by Miúra et al. (1975). In the region of color zoning, it is found that thickness of alternate lamellae and composition change mutually and remarkably. For the specimen showing color zoning in smaller region, it is extremely difficult to find a one-to-one correlation between An content and iridescence color which agrees with the Bøggild rule. In the region of smaller color zoning it is possible to find that blue region contains only 2–3% less An content than the red one. In color zoning through a few millimeters area, however, the compositional difference between blue and red regions is about 7 mole % An. An content obtained by electron probe microanalysis in the smaller region of red-iridescence shows lower value than that in the wider red region showing uniform iridescence color.
