Abstract

Combined data from electron microscope, electron microprobe, and ion microprobe analyzers can be used to determine the composition and thickness of lamellae in peristerite and cryptoperthite feldspars. Blue iridescent peristerite from Hybla, Ontario has a bulk composition of An5Or1, and lamellae compositions of An2Or1 and An19Or1. Orange-red iridescent peristerite from the same location has a bulk composition of An7Or1, and lamellae of An2Or1 and An23Or3. Two pale blue iridescent cryptoperthites from Quebec and Johana, Japan have the following compositions: An11Or30 (bulk) and An19Or15, An0Or51 for lamellae; An1Or50 (bulk) and An6Or35, An0Or72 for lamellae. The irregular nature of the lamellae in peristerites and cryptoperthites precludes ion microprobe depth profiling, such as has been applied to more regular labradorite lamellae. Point analysis must be performed instead, which may result in possible overlap onto adjacent lamellae the extreme limits.

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