436 W. F. Hillebrand — Analyses of three 



In places where the rock is most fractured and crushed the 

 descloizite appears in greatest quantity and finest condition as 

 an incrustation on quartz, often covering large surfaces, and in 

 color varying from yellow through all shades of orange-red to 

 deep reddish brown, the last named colors predominating. The 

 black color so frequent in descloizite from Lake Valley, New 

 Mexico, caused by a superficial coating or admixture of pyro- 

 lusite, is so far as my observation extended, wanting, hence 

 specimens from Georgetown are likely to be much sought after 

 for their showy appearance. A specimen in one of the banks 

 at Silver City, New Mexico, taken from one of the Georgetown 

 mines, resembled a stalactite in form. It was probably fully 

 three feet in height by six to eight inches or more in diameter, 

 and was deep reddish brown in color. 



The incrustations are for the greater part distinctly crystal- 

 line and are generally made up of aggregates of more or less 

 globular forms of a size ranging from microscopic to a diameter 

 of one or two millimeters. Each of these is composed of a 

 great number of apparently flat crystals, intergrown, and pro- 

 jecting sufficiently from the surface to give brilliant reflections 

 when observed under the lens, and to the naked eye a frosted 

 appearance where the globular growths are largest. The 

 richest reddish brown color is always coincident with this 

 development in size. The globular character changes fre- 

 quently to acicular. In such cases the incrustation seems to 

 have originally formed on bunches of radiating acicular, almost 

 colorless, vanadinite, which frequently appears thus coating the 

 quartz and running under the descloizite incrustations. Some- 

 times the vanadinite has entirely disappeared, and then there 

 may be a hollow through the center of the descloizite needle. 



The occurrence of vanadate of lead in the MacGregor mine at 

 Georgetown has been noticed by Professor Genth (1. c, p. 38). 

 The S2)ecific gravity of the mineral was not determined ; the 

 hardness is about 3*5 ; the color of the powder is orange- 

 yellow. An analysis gave the following results after deduct- 

 ing 11-91 per cent of insoluble matter, almost entirely quartz. 





56-01 





Molecular ratios. 





PbO 



2512 "1 







CuO 



FeO 



1-05 

 0-07 



oiioh 843 



•4788 



4-12 



ZnO 



17-73 



2189J 







V2O5---- 



20-44 



1119 ) 

 0041 J- -1178 







AS0O5--- 



0-94 



•1162 



1-00 



P 2 6 .... 



0-26 



0018 ) 







H 2 .... 



2.45 



1361 



•1361 



1-17 



CI 



0-04' 



0011 







Si0 2 .... 



1-01 









CaO 



0-04 









MgO 



003 









100-07 



