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Volume 4, pages 116-118, 1919


 EDGAR T. WHERRY . Washington, D. C.

      The crystals of chalcopyrite mentioned by Mr. Manchester in the preceding papers as brought to view by dissolving out calcite vein material proved to be well suited to crystallographic measurement, which was undertaken by the writer, using a Goldschmidt 2-circle goniometer. Two types were found to be represented. 

     In Type 1, the average development of which is shown in figure 1, the unit sphenoid, p (111) is dominant. The negative unit sphenoid, p, (111), is always present as small to medium sized faces, and the base, c, (001), as a well marked narrow face. In addition the prisms a (100) and m (110) are distinctly developed, tho mostly only in the midst of striations, and the second-order pyramid a (011) occurs similarly, in marginal striations. The figure shows, in somewhat idealized manner, the positions of these forms and of the striations observed on a single crystal.  

     The other, more complex and more abundant, habit, is shown in figure 2, again in average development. Three crystals of this type were measured, and the forms proved to be the same on all of them, the only difference being in the length of the dominant sphenoid from one to the other. The dominant sphenoid in this case appears to be r (332), altho this form does not yield particularly sharp reflections, but grades almost imperceptibly into the steeper form t (221) and this in turn into the prism w (110). The chief termination is the scalenohedron y (133), which grades into the second order pyramid a (001). In addition, both the positive and negative unit sphenoids p (111) and p, (111) are present, not as separate faces, but as well marked surfaces on striations so deep as to produce pyramid-like elevations at junctions between the dominant faces, as shown in the figure. 

     The angles actually observed on the four crystals studied are compared with the theoretical ones in table 1. It is noteworthy that the value of axial ratio c indicated, 0.997, is slightly greater than the accepted one (c = 0.9853) but all the faces are more or less rounded and striated, so that there is no reason to regard this as significant. Dana's orientation is, in the opinion of the writer, preferable to that adopted by Goldschmidt in the Winkeltabellen, the two differing by a revolution of 45° around the c axis; the symbols and angles have been adjusted accordingly. 


1 The Minerals of the Bergen Archways, Am. Min., 4 (9), 110, 1919.

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