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



The crystals of chromo-wulfenite from Ruskberg are 1-2 millimetres in 

 size. Most of them are quadrilateral pyramids, formed by the planese(l 1); 

 in some of them the pyramid is truncated by the terminal plane c(90 1). 

 The planes are convex. My measurements gave : — 



For crystal I. For crystal II. 



ce=57° 30' <?e=65° 10 f 



e<?'=73° 30 f . 



I did not succeed in finding in the crystals from Phenixville the form 

 alleged by Prof. Dana (Mineralogy, 1868). Those before me exhibit 

 the pyramid n, common to all wulfenites, assuming a tabular shape by the 

 development of the truncating terminal plane c (0 1). Their surface is 

 opaque, rough, and curved, thus manifesting, as it were, the resistance op- 

 posed to regular development of the fundamental form, by the accession 

 of heterogeneous substances. One of these crystals offered, besides the 

 planes c (0 1) and n (1 1 1), two other planes, m (1 1 0) and/(3 2 0), the 

 last of them in hemihedral development. I found on this last crystal : — 



By measurement. By calculation. 



nn=48° 30' nn = 48° 25' 



mwz = 24° 20' nm = 24° 12J' 



rc/=26° 50' nf=26° 35'. 



As the results of measurements show, this crystallographical revision of 

 chromo-wulfenites afforded no data for ascertaining the action of chromium 

 on the molybdate of lead ; they, however, confirmed the fact that the cha- 

 racteristic forms of eosite are wanting in the red varieties of wulfenite. 



§ 8. Discussion of Results. 



As a perusal of the last paragraph, treating of the morphological proper- 

 ties, will prove, these properties run parallel to the chemical characters of 

 the minerals here in question. The results obtained may be concisely 

 enounced thus : — 



The crystalline form of eosite differs from those of descloizite and 

 wulfenite, having the terminal lateral angles of descloizite united with the 

 crystallographical system of wulfenite. 



Eosite is a vanado-molybdate of lead. 



The red varieties of wulfenite have an admixture of chromium, but are not 

 crystallographically different from the other varieties. 



Descloizite is isomorphous with anglesite ; thus the results of the analysis 

 of descloizite seem to be questionable. 



The dark variety of vanadinite (A) from Kappel is identical with Peruvian 

 descloizite ; the light variety (B) from the same locality is nearly identical 

 in chemical characters with the dechenite of Schlettenbach and, as to the 

 form of its crystals, with descloizite. 



