THE MINERALS OF IDAHO 429 



verulent deep blue alteration product. The cleavage parallel to 

 £(010) is very prominent, yielding flexible laminae. Under the 

 microscope the pleochroism of some grains is very striking and 

 beautiful. 



IDAHO COUNTY 



A specimen from the Gold Hill property in the Dixie district con- 

 tains vivianite in the form of broad blue plates coating fractures in 

 an altered dike rock. 



OWYHEE COUNTY 



Vivianite has been observed in colorless to deep blue crystals in 

 clay in the Trade Dollar, Black Jack, and other silver mines of the 

 Silver City district in Owyhee County. A crystal from this district 

 which is now in the Field- Columbian Museum has been described by 

 Farrington and Tillotson. 31 The crystal measures 35 by 17 by 1 1 mm. 

 in size and is completely developed with the habit shown in Figure 

 141. It is transparent and dark green by transmitted and azure 

 blue by reflected light. The forms present are a(100), 6(010, ra(110), 

 w(101), andr(lll). The angles measured with a contact goniometer 

 on this crystal are below compared with the calculated angles: 



a(100) :m(110). 

 a'(100) :u>(101). 

 6(010) :»(111).. 



Measured Calculated 



36 30 

 56 00 

 58 00 



35 59 

 54 40 

 60 13 



ERYTHRITE (601) 

 COBALT BLOOM 



Hydrous cobalt arsenate, 3CoO.As 2 8 .8H 2 0. Monoclinic. 



Erythrite is a prominent mineral in the cobalt mines of the Black- 

 bird district and it has recently been identified from a locality in 

 Shoshone County. 



LEMHI COUNTY 



Cobalt bloom occurs as an earthy incrustation of pink and pearl- 

 gray color on the outcrops of cobalt deposits of the Blackbird dis- 

 trict. In places, as on the Beliel group, this mineral is so abundant 

 on the faces of cliffs that it can be seen for half a mile or more. 32 A 

 specimen collected by Mr. Frank L. Hess of the United States Geo- 

 logical Survey from the Haynes Stellite Co.'s mine consists of black 

 tourmaline-quartz rock containing fibrous coatings of beautiful rose- 

 red erythrite along seams and cracks. 



3i O. C. Farrington and U. W. Tillotson, jr. Field Columbian Museum Publications, Geological Series 

 vol. 3, p. 163, 1908° 

 » J. B. Umpleby. U. S. Geol. Survey, Bull. 528, p. 77, 1913. 



