F A. Genth — Contributions to Mineralogy . 119 



tained at each, the Copper Mountain Mine near Morenci, 

 Graham County, Arizona, and at Copperopolis, formerly the 

 American Eagle Mine, Tintic District, Utah. They very 

 kindly placed all their material at my disposal which enabled 

 me to make a fuller investigation and clear away the doubts 

 existing as to the constitution of this mineral. 



1. The Arizona mineral forms narrow seams in a siliceous 

 gangue, coated with earthy varieties of limonite. The lettso- 

 mite occurs in incrustations up to a thickness of about 2 mm . 

 In small cavities it shows thin fibers and small tufts often with 

 a radiated structure. Its color is from a deep sky-blue to 

 azure-blue; luster silky. Sp. grav. taken in alcohol 2*737. 



Some of the lettsomite has undergone an alteration, begin- 

 ning with a change into greenish yellow, and finally, by the loss 

 of the cupric oxide, into a fibrous yellowish white mineral. 

 At portions where the alteration has taken place the matrix is 

 frequently coated with a cryptocrystalline, mammillary hydrous 

 aluminum sulphate. Neither could be obtained in a quantity 

 sufficient for a fuller investigation. 



The analyses were made with almost pure azure-blue tufts 

 (a) and nearly pure sky-blue radiating particles {b and c). 



H ; 0. not det'd ) „...,. 21-89 21'89 1-216 78 8 



S0 3 12-38 f 12-59 12-49 0-156 1 1 



a b c Mean. Mol. Eatio. 



Insoluble 0-46 0-38 0'48 0'44 



t'd) 



38 J 



CuO 47-40 46-34 46"39 46-71 0-590 3-8 4 



A1 2 3 -. 15-71 16-94 16-77 16-47 0-161 ) . „ 



Fe 2 3 --- 0-80 1-61 1-64 1-34 0-088 [ 1U L 



99-74 99-76 99-34 



Considering the slight loss of cupric oxide by beginning 

 alteration, the ratio for S0 3 : CuO : A1 2 3 : H 2 is 1 : 4/: 1 : 8= 



Cu 4 Al,(OR) 12 . S0 4 -}-2H 2 0, which gives the following percent- 

 age composition : 



A1 2 3 102 15-88 



SO,... 80 12-56 



4CuO 316 49-23 



8H„0 ... 144 22-43 



642 100-00 



2. The lettsomite from the American Eagle Mine occurs 

 upon a bluish green mineral, which appears to be amorphous, 

 clay-like, and evidently a mixture of clay and lettsomite. The 

 pure lettsomite forms a velvet-like coating of azure-blue silky 

 fibers. The specimen being very small, only 0*055 grms. 

 could be obtained for analysis, which gave : 



