424 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



CUSTER COUNTY 



A mineral identified as mimetite occurs as minute yellow prismatic 

 crystals in a cavity in galena-tetrahedrite ore from the Ramshorn 

 mine, Bayhorse district (Cat. No. 56520, U.S.N.M.). Under the 

 microscope these are seen to be hexagonal prisms terminated by a 

 hexagonal pyramid which gave as an average for its p angle 40° 25' 

 against the calculated value for (10T1) for mimetite which is 40° 02'. 

 The mimetite crystals rest upon white cerusite crystals and are 

 largely replaced by the lead-copper arsenate bayldonite (q. v.). 



VANADINITE (552) 



Chlor-vanadate of lead, Hexagonal. 



9PbO.V 2 5 .3PbCl 2 . 



Only a single locality for vanadinite has been authentically re- 

 ported from Idaho, in the Spring Mountain district in Lemhi County. 

 Vanadate is reported from the Dixie district in 

 Idaho County, but specimens of the supposed vana- 

 dinite proved upon examination to be pyromorphite. 



LEMHI COUNTY 



Vanadinite has been identified by Mr. H. T. 

 Stearns in a specimen collected in the tunnel of the 

 Iron Mask mine, owned by William Clark of 

 Leadore, on Spring Mountain in the Spring Moun- 

 tain district. 28 The mineral forms yellow-brown 

 tabular crystals up to 2 mm. broad by 3^2 m m. thick 

 on manganiferous limonite. A crystal measured by 

 the present writer from Mr. Stearns' specimen was 

 bounded by the base c(000l) and the prism a(10T0) 

 with very narrow beveling line faces of the prism 

 6(1120) and the pyramid x(10Tl). The p angle for 

 the pyramid measured is 39° 28', which compares 

 well with the calculated value for vanadinite, which 

 is 39° 26'. Vanadium was found qualitatively in 

 the mineral by Mr. Stearns and Frank L. Hess. 



Fig. 137.— Olivenite 

 crystal, showing 



NEW FORM (043). 



Blackbird dis- 

 trict. Lem hi 

 County. 



Hydrous copper arsenate, 

 4CuO.As 2 5 .H 2 0. 



OLIVENITE (561) 



LEMHI COUNTY 



Orthorhornbic. 



Olivenite has been identified in a specimen from the Nickel Plate 

 mine on the Little Deer Creek side of the divide, 2 miles northeast 

 of the Uncle Sam mine in the Blackbird district. It forms druses of 

 dark olive-green crystals of small size in cavities in a cellular quartz 

 matrix containing residual granular patches of cobaltite. The oliven- 



28 Harold T. Stearns. Note on the first discovery of vanadinite in Idaho. American Mineralogist, 

 vol. 8, pp. 127-128, 1923. 



