In a recent paper in this journal1 entitled “The Optical Properties and Morphology of Bisbeeite,” Professor Austin F. Rogers described a blue mineral, occurring as minute fibrous spherulites in the Grandview mine, Grand Canyon, Arizona. His identification of the material as representing this species was based on the agreement of his optical data with that for bisbeeite, as determined by W. T. Schaller and recorded in Dana, Appendix 3, p. 14; however, Dr. Schaller informs the writer that the value of 1.65 there given for γ represents an intermediate value between β and γ Although E. S. Larsen2 definitely states that he used the original material for a more precise determination of the properties given, Rogers considers it “doubtful whether he worked with the original material.” Dr. Larsen informs the writer that not only is his published statement correct, but that he has recently redetermined the values, completely confirming his previous data.

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