178 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



contains grayish, phenocrysts of quartz which are rounded dihexagonal 

 pyramids. 



Custer County. — Euhedral doubly terminated crystals of quartz up 

 to an inch or more in length occur embedded in siderite of ores of the 

 Bay Horse district. These are sometimes somewhat milky and show 

 zonal growth lines. 70 Near Challis quartz occurs in small amount 

 coating platy (argentine) calcite and as spherulitic and spindle- 

 shaped microscopic grains associated with ptilolite. 71 In the cirque 

 at the head of Wildhorse Canyon at the eastern base of Hyndman 

 Peak quartz occurs in crusts of clear transparent crystals lining many 

 hollow veins in quartzite and gneiss. In basaltic lavas at many 

 places in the upper valley of Lost River clear transparent quartz 

 crystals line chalcedony geodes weathered out of the lava. These 

 crystal-lined geodes are sometimes a foot in diameter. 



Elmore County. — Vuggy quartz in veins of the Vishnu mine, Rocky 

 Bar district, contains small crystals of quartz. 



Owyhee County.— The gangue of the silver veins of the Silver City 

 and adjacent districts in Owyhee county contains large amounts of 

 quartz which is in part crystalline, in part chalcedonic and, in the De 

 Lamar district, pseudomorphous, as described below. Numerous 

 cavities and vugs occur in the ores and these are frequently lined 

 with druses or larger crystals of transparent quartz, frequently 

 intimately associated with ore minerals (pi. 3, lower). Fine crystals 

 forming a continuous crust are to be found on the Blaine tunnel 

 dump, Silver City district, and the Banner vein on Long Gulch, 

 % mile south of Silver City, contains numerous vugs lined with 

 beautiful quartz crystals. A specimen from the Silver City mine 

 consisting of a quartz-adularia intergrowth contains cavities lined 

 with transparent colorless quartz crystals 3 to 5 mm. long which 

 are prisms terminated by only three faces of one rhombohedron. 

 Crystals of this same habit occur also in ore from the Mahogany mine 

 (Cat. No. 14776, U.S.N. M.). Much of the pseudomorphous quartz 

 from the De Lamar mine contains drusy quartz in minute crystals. 



Lemhi County. — Fine druses of small quartz crystals have been seen 

 coating galena in ore from the Pittsburg-Idaho mine, Gilmore district. 



Shoshone County. — Fine sparkling specimens of drusy quartz 

 coating chalcopyrite occur in the ore of the Empire (Horst-Powell) 

 mine on the Little North Fork of the Coeur d'Alene River. 



c. AMETHYST 



Amethyst is essentially the same as rock crystal except that the 

 crystals are colored purple, probably by small amounts of manganese. 

 Amethystine quartz crystals have been noted in Idaho lining chalce- 



™ J. B. Umpleby. U. S. Geol. Survey, Bull. 539, pi. 7, 1913. 



« Clarence S. Ross and Earl V. Shannon. Proc. U. S. Nat. Museum, vol. 64, Art. 19, 1923. 



