E. B. Hurlburt — Alunite from Colorado. 131 



which is considerably higher than that given by other authors 

 for alunite. 



The results of the analysis are as follows : 



Theory where 

 Ratio. K:Na:4:7 



S0 3 38-93 -486 4 -00 39-65 



Al 2 3 39-03 '382 3-12 3*7-93 



ICO 4-26 -042) 4-21 



Na 2 4-41 -075f ll/ J ° 4-83 



H 2 1335 -741... 6-07 13-38 



Insol ._ *50 



100-48 100-00 



The ratio of S0 3 : A1 2 3 :(K + Na) 2 : H 2 is very nearly 

 4:3:1:6 as required by the commonly accepted formula of 

 alunite KAl 3 S 2 O n , 3H 2 0. The agreement between the theory 

 and analysis is satisfactory. The mineral suffers no loss by 

 heating in an air bath at 300° C. and water is first given off 

 at a temperature near redness. It is therefore to be regarded 

 as water of constitution and the formula should be written 

 K[A1(0H) 2 ] 3 (S0 4 ), 



An interesting feature of this analysis is the large percent- 

 age of sodium, the ratio of K : JSTa being about 4 : 7, while 

 alunite has usually been regarded as a potash compound only. 

 Another interesting feature is the insolubility of the mineral 

 in hydrochloric acid. By digesting for two weeks on the 

 water bath 13-30 per cent of the mineral and 3*84 per cent of 

 S0 3 went into solution. 



The occurrence of alunite from the Rosita Hills in Colorado 

 has been mentioned by Gross,* who regards its formation as 

 the result of solfataric action on rhyolite. The material de- 

 scribed by him consisted of immense rock masses made up 

 essentially of alunite and quartz. He cites an analysis of 

 nearly pure white crystals made by Eakins in which the ratio 

 of K : Na, was found to be nearly 4 : 7 corresponding to the 

 material from Red Mountain. The origin of the mineral 

 from this last locality is probably similar to that from the 

 Rosita Hills. 



In closing the author desires to express his thanks to 

 Professor Penfiekl for valuable advice during the progress of 

 this examination. 



Laboratory of Mineralogy and Petrography, 

 Sheffield Scientific School, 1894. 



* This Journal, III, xli, p. 466, 1891. 



