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概要

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Iridescence observed in Gem labradorite stone, i.e., Iabradorescence, has been studied experimentally. From spectral distributions of labradorescence and electron microscopical observations, it is found that Gem labradorite from deep-seated plutonic and metamorphic rocks exhibits periodic lamellar structure, and that the Bipggild rule holds for Gem labradorite with compositions from An_<49> to An_<58> i.e. , characteristic colour changes Lrom U. V. to Near IR as Anorthite (An) content increases. In the region showing "colour zoning" where thicknesses of alternate lamellae and An content are remarkably variable from place to place, it is difficult to obtain one to one correlation of the Bipggild rule. From microanalysis of lamellae with an analytical electron microscope (JEM-100C/SEG/ASI DlNDS) and ion microprobe mass analyzer (IMA-2) confirmed that the mean chemical compositions of An-poor and An-rich lamellae are An_<44(±4)> Or_<3(±1) >and An_<58(±6)> Or_<2(±1)>, respectively. The mean composition difference between adjacent lamellae is 15 percent An and I percent Or. Labradorescence is, therefore, infered to the lamellar multilayer which consists of two periodically stratiLied lamellar structure having different compositions and thicknesses of the order of a few hundred nanometers.
宝石学会(日本)の論文
1977-12-15