462 Dr. A. Schrauf on Molybdates and Vanadates of Lead. [May 4, 



impossible to detach any complete crystal out of them. Here and there 

 isolated lateral angles, some of them offering an angle of about 90°, are 

 distinguishable. 



As to the form of crystals, the variety B of vanadinite from Kappel bears 

 some resemblance with these aggregations of dechenite. Some few solid 

 angles of the variety B could be detached and their angles measured. The 

 results thus obtained are : — 



Crystal I. Crystal II. Crystal III. 



p:p'z=90° p:p = 52° p:'<p=64i° 



p: p'=9l° 

 'p: p' = 127°. 



These angles are perfectly concordant with those obtained by my former 

 measurements (see Poggendorff's Ann. vol. cxvi.), as well as with those at 

 present taken on the crystals of the dark variety A from Kappel. These 

 last gave : 



For crystal III. 



For crystal I. For crystal II. (with the planes p and m). 



p:'p= 65° p: >= 64° 50' p:p' = 91° 30' 



p:p'= 92° 'p:'p'= 90° 'p:'p'= 90° 50' 



>:/ = 128° 'p':p'= 63° 30' p:p= 53° 30' 



jo': p= 90° ? : $= 65 ° °' 



>' : 'p =116° 10' m: m' = U6° 30' 



~ v : 'p = 53° p:m= 32° 50' 



p : >'=127° 



All these numbers are in . perfect concordance with those ascertained by 

 M. Des Cloizeaux on the Peruvian descloizite ; these are : — 



mm =116° 25' 



m H = 147°45' 

 b\b\=\2T 10' 

 b±{m)b±=\\b° 15' 

 b\ (4) b±= 88° 18'. 



These results prove thus the absolute identity of the forms of Peruvian 

 descloizite with those of both varieties of vanadinite from Kappel, probably 

 also with those of dechenite, all of them discrepant from the characteristic 

 forms of eosite. These investigations throw likewise some light on the 

 indices of the planes observed on descloizite. 



M. Des Cloizeaux has observed the three planes m b\ and ef , whose indices 

 are, (1 1 0), (1 1 1), and (2 3). M. Des Cloizeaux expressly states that 

 he could not find out from these data any isomorphism between this form 

 and that of any other lead salt. I can, however, in no way explain how so 

 eminent a mineralogist came to omit comparing the parameter of anglesite 

 with that of descloizite, as be did with the parameter of cerussite. 



