THE MINERALS OF IDAHO 321 



to be made up mostly of andalusite with some quartz, phlogopite, 

 sericite, magnetite, and rutile. 49 



CYANITE (400) 



Aluminium silicate, Al 2 3 .Si0 2 . Triclinic 



The only important locality for cyanite thus far known in Idaho 

 is in Shoshone County. 



SHOSHONE COUNTY 



Cyanite is frequently developed in metamorphosed sedimentary 

 rocks of the Belt series in the southern portion of Shoshone County, 

 especially in the southern half of the area of the Avery topographic 

 sheet. The mineral occurs in micaceous schists as prismatic rude 

 crystals, some of which reach a length of 30 cm. Many of these are 

 coated on the outside with mica and a considerable proportion of 

 them are completely altered to pseudomorphs of mica. Fine speci- 

 mens may be obtained in places. Some specimens, the exact locality 

 for which was not learned, contain abundant fine blue blades in 

 small segregated quartz veins and green blades in micaceous schist 

 adjacent to such veins. A specimen from 2*/£ miles south of Trimmed 

 Tree Mountain contains pale blue blades of cyanite up to 5 mm. in 

 width by 3 cm. in length in a coarse matrix of chlorite, biotite, feld- 

 spar, and black tourmaline. 



GADOLINITE (404) 



Basic silicate of beryllium, iron, and 



yttrium, approximating the formula Monoclinic. 



2BeO.Fe0.2Yt 2 3 .2Si0 2 . 



The only reference to the occurrence of the rare earth mineral 

 gadolinite in Idaho is found in an analysis published in a Russian 

 journal. 50 The locality of the mineral is not given more definitely 

 than simply Idaho in North America. The gadolinite analyzed had 

 a specific gravity of 4.382. The analysis gave the following results: 



Analysis of gadolinite from Idaho 



(G. Chernik (Tschernick), analyst) 



Per cent 



Beryllium oxide (BeO) 9. 98 



Ferrous iron (FeO) 12. 74 



Magnesia (MgO) . 21 



Lime (CaO) . 60 



Silica (Si0 2 ) 24. 41 



Thoria (Th0 2 ) . 30 



Yttria (Y 2 3 ) 42. 94 



Ceria (Ce 2 3 ) 1-94 



49 E. S. Larsen and D. C. Livingston. Geology of the Yellow Pine mining district, Idaho. U. S. Oeol. 

 Survey, Bull. 715, p. 78, 1920. 



»• Chernik. Journ. Soc. Phys. Chim. Russe., vol. 36, pp. 25-27 and 287-301, 1904; abstract Zeitschr 

 Kryst. vol. 43, p 78, 1907. 



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