Penfield and Ford — Calaverite. 24-1 



not cause discrepancies in the angles greater than the character 

 of the reflections would seem to warrant. It is probable that 

 some of the symbols will need revision and change. The 

 crystals which we have been able to examine are such as might 

 be designated as good, though they are not of the very best 

 quality. It should be explained also that all of the crystals in 

 our possession have been studied and all of the results given, 

 not merely a selection of best values. If one could have a 

 larger variety of occurrences to select from, it is likely that 

 some exceptionally good crystals might be found from which 

 more exact and reliable measurements could be obtained. A 

 careful study of such crystals would be of great value, for the 

 correctness of the complex symbols indicated by the measure- 

 ments made by us needs verification. One especially note- 

 worthy feature of the symbols as given by us is that eleven, or 

 some multiple of it, appears in many of them ; though the 

 significance of this, if there is any, is not apparent. 



It is possible that by adopting another orientation some sim- 

 plification of the symbols may result. The chances for bring- 

 ing about much simplification, however, do not seem to be 

 very promising, and any change in orientation must necessa- 

 rily do away with the apparent similarity in crystallization 

 between calaverite and sylvanite, as indicated by us on page 

 240. 



It was noted in a recent number of Nature* that Mr. G. F. 

 Herbert Smith had discussed crystals of calaverite before the 

 Mineralogical Society of London, and described them as " tri- 

 clinic, but pseudo-monoclinic owing to twinning about an axis 

 parallel to the prismatic zone." Upon observing this, we 

 immediately communicated with Mr. Smith, sending him the 

 results of our investigation, and he in reply has kindly sent us 

 a brief statement of his work. He expects soon to publish his 

 results, and we do not feel at liberty to discuss them at this 

 time. It may be stated, however, that he has in the three- 

 circle goniometer recently described by him* an instrument, 

 regarded as especially adapted to the study of such complex 

 crystals as those of calaverite, by means of which he is able to 

 discover zonal relations which ordinarily would escape detec- 

 tion. From the study of these he is led to assign simple 

 indices to the majority of the forms, which necessitates, how- 

 ever, the assumption of triclinic symmetry and a peculiar 

 twinning. As far as the angles and the distribution of the 

 faces are concerned, his crystals, like ours, evidently satisfy the 

 conditions of monoclinic symmetry. We quote the following 



* Vol. Ixlii, p. 555, 1901. 



■f Min. Mag., vol. xii, p. 175, 1899. 



