THE MINERALS OF IDAHO 431 



from a prospect 1 mile from the mouth of Slate Creek near Avery in 

 the St. Joe Basin in Shoshone County. The crythrite occurs as 

 crusts and druses of rose pink crystals which are too small for meas- 

 urement. Under the microscope these are lath-shaped and are 

 optically biaxial with 2V large. The extinction ZAc is —33°. The 

 mineral is pleochroic with Y = colorless, Z = brownish pink. The 

 acute bisectrix is perpendicular to the flat cleavage fragments. The 

 mean refractive index /3 is 1.660, ±0.002. 



ANNABERGITE (602) 



NICKEL BLOOM 



Hydrous nickel arsenate, 3NiO.As 2 5 . 8H 2 0. Monoclinic. 



The only reported locality for the nickel arsenate is in the Blackbird 

 district in Lemhi County. 



LEMHI COUNTY 



Annabergite is reported to occur with erythrite as a conspicuous 

 constituent of the outcrops of the cobalt deposits of the Blackbird 

 district. 33 It is probable that the identification is not definite, but 

 is based by analogy with the occurrence of erythrite. Such green 

 arsenates as have been examined from this district contain no nickel 

 and, considering the very small amount of nickel in the primary 

 ores, annabergite must be very rare, if it occurs at all. A specimen 

 labeled "Nickel bloom," from the Alpha claim, stated to occur 

 abundantly as float on the surface of the divide and to be typical 

 of material occurring commonly at most of the prospects in the camp, 

 consists of ferric iron arsenate with some copper, probably principally 

 in the form of scorodite. It contains no trace of cobalt or nickel. 

 Another green alteration product surrounding residual patches of 

 cobalt in ore from the Nickel Plate claim consists of a mixture of 

 olivenite and scorodite and contains no nickel. 



SCORODITE (607) 



Ferric iron arsenate, Fe2O3.As2O5.4H2O. Orthorhombic. 



Scorodite is probably a mineral of common occurrence in Idaho in 

 thin yellowish to green films and stains which have resulted from 

 the oxidation of arsenopyrite. In a few places in the State it has 

 been found in larger and better characterized masses. The optical 

 properties of the mineral are so variable and the mineral so fre- 

 quently occurs as cryptocrystalline or very fine-grained aggregates 

 that it is almost impossible to determine or identify the mineral 

 optically. The principal localities from which the mineral has been 

 obtained are as follows: 



» J. B. Umpleby. U. S. Ocol. Survey, Bull. 528. p. 75, 1913. 



