460 Dr. A. Schrauf on Molybdates and Vanadates of Leal [May 4, 



and may be identified with the dechenite from Schlettenbach. Eosite 

 differs from both these minerals as to its chemical characters. 



§ 5. Crystallographical form of Eosite, 

 Nearly all the eosite crystals attached to the surface of the cabinet spe- 

 cimen are octahedra, three-fourths of which are completely developed, only 

 one of them showing one angle truncated by the basal plane c (0 1). 

 The planes, instead of being completely even, are somewhat bent and 

 scaly; however minute the planes p (1 1 1) and c (0 1) are, the intense 

 metallic brightness of the crystals admits a precise determination of the 

 angles. 



The angles ascertained by measurement are : 



Crystal L {p (1 1 1)}. Crystal II. {p (1 1 1)}. Crystal III. {c (00 1) ; p (1 1 1)}. 

 p : p = 53° 30' p : > = 77° 30' c : p = 63° 20' 



jp:'_p=102° 50' 'pi ^ = 102° 10' ci'p = 62° 30' 



'p:p=l03° pip'= 77° 50' c: p'= 62° 50' 



pi'p^ 77° 50' 'pip =103° 25' 



pip = 53° 50' 

 pi p'= 77° 30' 

 pi'p =102° 



The means of these results are : — 



c:p=(00 1)(l 1 1)=65° 50' 

 pi'p=(\ 1 l)(Fl 1) = 77°50', 



(1 1 1):(10 1)=38°55' 

 (1 1 1): (I 1 0)=2/° 10' 

 (1 1 1):(100) = 51° 5' 

 (1 0) : (1 1 0)=45° 5'. 



The preceding data lead to the parametrical proportion 



0=1*003:1: 1-375, 



not very far different from a pyramidal axial proportion. The last- quoted 

 prismatic angle differs also only by 5' from the pyramidal principal prism. 

 Notwithstanding the prisms with an angle of 90° 10' being proper to 

 several prismatic minerals, the slight difference obtained in the present 

 case may be ascribed to an error of observation, owing to the exiguity and 

 the curved surface of the planes, and eosite may be safely ranked among 

 the pyramidal system, with the axial proportion 



a: a: c=l : 1 : 1-3758, cp=62° 50.'. 



This parametrical proportion of eosite, together with its. chemical cha- 

 racters, proves its near relation to wulfenite and descloizite, Eosite unites 



and consequently 



