The discovery of a new locality for pyroxmangite provided material for a rather complete study of this little-known triclinic manganese and iron pyroxene, and established Idaho as a second occurrence of the mineral in America. Physical, optical, chemical, and x-ray properties of the new mineral show close agreement with those of the mineral from the original locality at Iva, South Carolina. The indices of refraction are slightly lower in the Idaho material, due probably to a correspondingly lower iron content. A careful study of the mineral from Sweden, called sobralite, revealed its identity with pyroxmangite, a name which has four years’ priority over sobralite. A comparative study of pyroxmangite with rhodonite (both iron-rich and iron-poor varieties) shows distinct differences in the birefringence and axial angle. X-ray patterns indicate a structural difference between the two minerals that, in the light of our present knowledge, justifies the retention of both mineral species. A complete structural analysis, however, may be necessary to establish the definite relationship of pyroxmangite to rhodonite.

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