464 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



doubtless formed by the action of the acid water of the sulphur 

 springs on the volcanic tuff in which the deposits occur. 



MENDOZITE (776) 



Hydrous sulphate of sodium and alu- Fibrous, 



minium, Na 2 O.Al 2 3 .4S04.24H 2 0. 



Although its existence here has not been established, mendozite 

 may occur in Owyhee County. 



OWYHEE COUNTY 



Just below the falls of Jump Creek there is a ferruginous zone 

 about 1 meter wide along which and to the north of which the rock 

 is much fractured. Just above this a little nitrate has been found 

 in a little recess which has been deepened by picking. The nitrate 

 has all been removed but crevices contain a white coarsely fibrous 

 prismatic salt in veinlets up to 2 cm. wide (pi. 30, upper) with a 

 strong astringent alum-like taste. A qualitative test shows very 

 little potash but abundant sodium, magnesium, and aluminium. 

 The substance is essentially a combination of the sulphates of these 

 three elements. 72 These sulphates may be present as alunogen, 

 mirabilite, and epsomite, but the characters of the material and the 

 astringent taste would seem to indicate that they are present as 

 alums, the magnesium as pickeringite, and the soda as mendozite. 

 This could be established by optical examination but no samples 

 have been available for study. 



PICKERINGITE (768) 



MAGNESIA ALUM 



Hydrous magnesium aluminium sul- Monoclinic. 



phate, MgO.Al 2 3 .4S0 3 .22H 2 0. 



Pickeringite probably occurs with other salts in Owyhee County, 

 as it has been definitely identified in the same region on the Oregon 

 side of the State line. 



OWYHEE COUNTY 



As has been mentioned above under mendozite there occurs in 

 crevices in rhyolite in a nitrate prospect just below the falls of Jump 

 Creek a white coarsely fibrous or prismatic salt in veinlets up to 1 

 cm. wide. This has been found to consist of sulphates of aluminium, 

 magnesium, and sodium and, from the fact that the material has a 

 strongly astringent taste like the alums it is presumed that they are 

 combined in the double sulphates with alumina, in which case the 

 magnesia is in the form of pickeringite. 73 



*» G. R. Mansfield. U. S. Geol. Survey, Bull. 620, pp. 24-25, 1916. 

 « G. R. Mansfield. U. S. Geol. Survey, Bull. 620, p. 24-25, 1916. 



