156 RE-EXAMINATION OF AMERICAN MINERALS. 



vanadic acid in the red varieties, and the intensity of color is 

 proportional to the amount of vanadic acid, which in no in- 

 stance is much more than one per cent. 

 The analyses afforded 



Yellow variety. Red variety. 



Molybdic acid 38.68 37.47 



Vanadic acid 1.28 



Oxide of lead 60.48 60.30 



99.16 99.05 



The second corresponds very nearly to 97 per cent, of molyb- 

 date and 3 per cent, of vanadate of lead. As the last substance 

 varies in quantity, it can not be regarded as giving a distinct 

 specific character to the mineral. This mineral has been de- 

 scribed as a chromo-molybdate of lead, but by the most careful 

 examination only a trace of chromium can be detected. In 

 fact, the quantity is so minute as to require further examina- 

 tion in larger quantities to place the matter beyond a doubt. 



Wulfenite occurs alone on crystallized and cellular quartz, 

 or associated with pyromorphite, whose beautiful green color 

 is often very much enhanced by the contrast of the yellow and 

 red crystals on its surface. 



Sometimes the wulfenite forms the mass, and crystals of 

 pyromorphite are sparsely disseminated over the surface. It 

 is also found in decomposed granite — on carbonate of lead and 

 oxide of manganese — also associated with vanadate of lead. 



51. Yanadate of Lead (Descloizite?). 

 This species has never before been remarked among Ameri- 

 can minerals, although the chloro-vanadate (vanadinite) was 

 first discovered in Mexico. This adds another to the list of 

 curious minerals from the Wheatley Mine. It was noticed 

 about a year ago in the form of a dark -colored crystalline 

 crust, covering the surface of some specimens of quartz and 

 ferruginous clay associated with other minerals. Observed 

 with a magnifying glass, it is seen to consist principally of 

 minute lenticular crystals, grouped together in small botry- 

 oidal masses. The crystalline structure is perfect. Thus seen, 

 the color of the mass is of a dark-purple, almost black. When 

 seen by transmitted light, the color is dark hyacinth-red and 

 translucent. The streak is dark-yellow. From the difficulty 

 of obtaining any quantity of sufficient purity, nothing accurate 



