1885.J <jt) J [Genth and Voni Hath. 



found before, and that arsenic and vanadium are present in the proportion 

 of 1 : 1. 



The change of color of these groups of crystals, however, appears to 

 indicate that the vauadiferous mimetite or endlichite may gradually change 

 into vanadinite. 



Probably the same mineral has already been observed by Prof. Silliman 

 at the Torrence Mine, Socorro, N. M., where it occurs in small yellow 

 hexagonal prisms which were mistaken for vanadinite, but were mimetite 

 containing vanadium. 



Desdoizite. 



The writer has just received from Prof. Gerhard vom Rath the following 

 communication which he gives in his own words : 



"The recently discovered crystals of this rare species surpass in perfec- 

 tion and development by far those from previously known localities. 

 They offered an opportunity to examine again the dift'erent opinions re- 

 garding their crystallographic system. (Des Cloizeaux, Ann. de chiniie 

 et de physique, 3 ser, 41,78 and Websky, Zeitsch. fiir Krystallographie 

 5,542.) ^ 



" If we retain the primitive form suggested by the distinguished French 

 crystallograplier, which has also been adopted by the celebrated Berlin 

 Professor, changing the system, however, which Des Cloizeaux supposed 

 to be rhombic, into monoclinic, we have these faces referred to the 

 rhombic system : 



" The fundamental angles have been measured as follows : 



0:0' (brachydiagonal edge) = 126° 56 

 " 0:0" (macrodiagonal edge) = 90 54 



" thence the proportion of the orthogonal axes ; 



a : b : c = 0.6367 : 1 : 0.8046. 



PROC. AMEK. PHILOS. SOC. XXII. 120. 2u. PRIISTED MAY 26, 1885. 



