82 Prof. Chapman on the Klaprothine 



Prof. T. Sterry Hunt, of the Geological Survey of Canada, I 

 propose in the present place to offer a brief notice of its leading 

 rnineralogical characters. 



All the earlier determinations of lazulite crystals referred the 

 mineral to the trimetric or rhombic system. Prufer of Vienna 

 was the first to maintain its monoclinic character ; and the angles 

 given in the more recent works on mineralogy are adopted from 

 his measurements. The European crystals present in general a 

 somewhat complicated aspect, although certain combinations 

 closely resemble those of the trimetric system. Two " augite 

 pairs " are always present. These, according to Prufer, measure 

 respectively over a front edge 100° 20' and 99° 40', the difference 

 being but little more than half a degree. According to the same 

 observer, moreover, the inclination of the base on the prism-plane 

 (0 P : co P, in the notation of Naumann) only differs from a 

 right angle by 23'. Were these values consequently all that we 

 had to depend upon, it would be manifestly unsafe to rely upon 

 them as proofs of the monoclinic crystallization of lazulite. But 

 in some combinations the forms below the middle zone of the 

 crystal are less numerous than those above this zone, or otherwise 

 differ from the latter in their measurements. Nevertheless in 

 certain trimetric minerals, and notably in datolite and Wolfram, 

 we have the same peculiarity, and Ave might therefore look upon 

 these lazulite crystals as trimetric combinations hemihedrally 

 modified. From my examination of the North Carolina speci- 

 mens, I cannot but think that this view will in the end prevail. 

 It is supported by the fact that in many combinations the upper 

 and lower forms do actually correspond in number and character, 

 and that practised crystallographers like Phillips and Levy, skilled 

 in the use of the goniometer, were unable to detect in their mea- 

 surements the differences announced by Prufer*. 



The North Carolina crystals (presuming those in my possession 

 to represent the generality of crystals obtained at this locality), 

 although usually distorted, are of extreme simplicity, contrast- 

 ing remarkably in this respect with the majority of European 

 examples. At first sight they resemble a monoclinic prism ter- 

 minated by a single "augite pair" or hemi-pyramid ; but they 

 really consist (if monoclinic) of two hemi-pyramids, the four 

 planes of one of which are greatly elongated; or if trimetric (as 

 I conceive them to be), they form a rhombic octahedron in which 

 four planes, in opposite sets of two, are thus lengthened beyond 



* These observers appear to be the only crystallographers who have 

 practically examined crystals of lazulite. Thus the measurements of Phil- 

 lips are followed by Hausmann, Breithaupt, and others ; those of Levy, by 

 Dufrenoy; and those of Prufer, by Naumann. Dana.Qucnstedt, and Miller. 



