194 C. A. Ingersoll — Hemimorphic Wulfenite Crystals. 



These crystals were small, measuring from one to two 

 millimeters in diameter, white in color, subtransparent, and 

 of a decided adamantine luster. * Before attempting to measure 

 any of them a careful blowpipe examination was made, and 

 the mineral was found to be Wulfenite. Three crystals were 

 selected as best representing the different habits of the min- 

 eral, and one of these (fig. 1) was chosen for cry stall ographic 

 measurement. This was quite perfect, prominently hemi- 



morphic in development, and more highly modified than any 

 of the others. Its faces yielded remarkably distinct reflec- 

 tions of the goniometer signal, thus furnishing very accurate 

 measurements of the interfacial angles. The forms that were 

 observed, together with their hemimorphic occurrence, are 

 as follows : 



c, 001, above and below. 

 n, 111, 1 " " " 

 w, 102, f* " 



e, 101, \-i above and below. 



p, 201, 2-i below only. 



7t, 313, III? above and below. 



Of the above forms j? and 7t were here observed for the first 

 time ; moreover, they were found only on a single crystal 



The hemimorphic character of the mineral is shown in 

 the occurrence of the p face, only in the lower portion of 

 the crystal, as well as in the relative development of the other 

 faces. The form it is present in the upper portion as a very 

 narrow face, while below it is quite well developed. On all 

 the crystals the lower c face is the larger, while the upper one 

 is sometimes wanting (fig. 3). The development of the forms 

 n and e on some of the crystals is very remarkable (figs. 2 and 

 3). A hemimorphic habit, similar to fig. 3, has already been 

 observed by Breithaupt* on crystals from Berggieshiibel in 

 Saxony, which are described by him as being beautifully 

 white, with adamantine luster. 



*Handbuch der Mineralogie, II, p. 272, 1841. 



