RE-EXAMINATION OF AMERICAN MINERALS. 157 



can be stated with reference to its specific gravity and hard- 

 ness; and for the purpose of analysis I was obliged to use ma- 

 terial which, although containing pure crystals of the vanadate, 

 was yet mixed with crystals of molybdate of lead and other 

 impurities. 



The chemical analysis is an imperfect one, yet the best that 

 can be made from the mineral as it has been found. It is as 

 follows : 



Vanadic acid 11.70 



MolyMic acid 20.14 



Oxide of lead 55.01 



Oxides of iron and manganese.. *) ^ qq 



Alumina / 



Oxide of copper 1.13 



Sand 2.21 



Water 2.94 



99.03 

 If we subtract the amount of oxide of lead requisite to form 

 wulfenite with the molybdic acid present, we have left 22.82 

 per cent., which is combined with 11.7 of vanadic acid, making 

 a compound corresponding to : vanadic acid, 66.1 ; oxide of lead, 

 33.9=100. 



This result is not considered precise. It corresponds, how- 

 ever, more nearly with the composition of descloizite, as given 

 by Damour (Pb 2 V=Y 29.3, pb . . . 70.7), than with dechenite by 

 Bergmann (Pb V=:V 45.34 Pb 54.66).* 



The composition of descloizite can not be considered as 

 having been fairly made out; for Damour's results are deduced, 

 as mine have been, from a very impure material, and may on 

 future examination prove to be Pb 3 V 2 ; corresponding in com- 

 position to the chromate of lead called melanochroite. This 

 mineral has as yet been found only in small quantity at this 

 mine, associated with oxide of manganese and wulfenite, the 

 crystals of this latter substance being more or less covered 

 with minute crystals of the vanadate. 



52. Pyromorphite. 



There are several shades of color belonging to this mineral ; 

 a green so dark as to be almost black, olive-green, pea-green, 

 leek-green, greenish yellow, and all intermediate shades. It 



* Descloizaux bas since verified this view by its crystalline form. 



