1871-] Dr. A. Schrauf on Molybdates and Vanadates of Lead. 463 



Such a comparison proves immediately the isomorphism of both these 

 minerals, the angles of anglesite being : 



n»'=115 6' 

 ay = 56° 51' 

 by= 45° 3' 

 cy = 63° 19', 



and those of descloizite : 



W=116° 25' 



= 44° 9' 

 = 63° 35' 



M. Des Cloizeaux's symbols must consequently be admitted as equiva- 

 lent* to 



m' = n (0 2 1) 

 &i=y(2 2 1) 

 4=^(3 01). 



These notations and symbols I intend to adopt in future. This disposi- 

 tion equalizes the terminal angles of eosite with those of descloizite, — [c y] 

 of descloizite being nearly equivalent to [c^] of eosite. 



This isomorphism of anglesite (PbOS0 3 ) with descloizite (2PbO,V0 3 

 according to M. Damour) is only to be accounted for by granting to M. 

 Damour's analysis less importance than its author's name allows to claim, 

 and by admitting descloizite, vanadinite, and dechenite to be merely mono- 

 vanadates. Thus another argument for separating these three minerals be- 

 comes untenable ; the only distinctive character still remaining is the greater 

 or lesser proportion of zinc contained in them. 



§ 7. Crystallographical form of the Chromo-Wulfenites. 



Prof. H. Rose, in his above- quoted investigation of the chromo-wulfenites, 

 has given the measures of angles of the variety from Beresowsk, differing 

 but slightly from the pyramidal angles generally admitted. I intend in 

 the present paper to ascertain the angles of the chromo-wulfenites from 

 Ruskberg and Phenixville, in order to state the changes arising from the ac- 

 cession of chromium to the constituting elements. The nature of the planes 

 is, however, such that the measurements offer differences of nearly the 

 averages from even a greater number of observations becoming thus rather 

 objectionable. 



* Concerning the indices and forms of anglesite, see my ' Atlas der Crystalformen 

 des Mineralreiches,' under the article " Anglesite." The isomorphism of descloizite 

 and anglesite appears in the similarity of forms, as well as in the equality of angles, 

 the vanadinite from Kappel resembling the anglesite from Siegen, as the Peruvian 

 descloizite is similar to .the anglesite from Wolfach. See Schrauf's ' Atlas der Crystal- 

 formen,' No. 2 (Vienna, 1870), tab. xi. fig. 1, and tab. xii. fig. 32. 



