206 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



masses of the mineral on the footwall side of the vein. Beautifully 

 botryoidal masses, with brilliant metallic-adamantine luster occurred 

 formerly in the ores of the Hercules mine at Burke; a compact, 

 massive variety was found on the sorting belt of the Last Chance 

 mine at Wardner in 1915, when much of the ore was coming from 

 above the No. 1 tunnel; and specimens are said to have been found 

 in the Bunker Hill open cut. 



The oxidized ores of the mines producing plattnerite have been 

 mostly exhausted. In the days when this mineral was found it was 

 believed to be iron and was usually discarded, so that a search of the 

 dumps of tunnels and cuts in the upper portions of these veins should 

 yield a number of good specimens, and lease workings in oxidized 

 ores should be carefully examined for this mineral. Good specimens 

 have not been found elsewhere in America than in the Coeur d'Alene 

 district and the locality in Lemhi County mentioned above, although 

 reported from South Dakota. Localities in Scotland and elsewhere 

 in Europe produced a few specimens many years ago, and its occur- 

 rence at Tsumeb, German wSouthwest Africa has been noted. Speci- 

 mens from the Mullan locality are now in all good collections through- 

 out the world. 



PYROLUSITE (254) 

 Manganese dioxide, Mn0 2 Orthorhombic . 



Pyrolusite and psilomelane are the two most common oxides of 

 manganese found in a great variety of situations. The principal 

 recognizable difference between these is that pyrolusite is commonly 

 crystalline in appearance and is lighter in color, while psilomelane 

 is usually black and amorphous. Of the occurrences of manganese 

 oxides noted in Idaho, in the absence of more definite determinations, 

 the ones showing distinctly crystalline structure are referred to 

 pyrolusite and the balance are placed under psilomelane. The iden- 

 tifications of other authors are copied without change, while descrip- 

 tions of manganese oxide without further detail are placed under 

 psilomelane. Although a number of occurrences are known, none is 

 economically important. 



BLAINE COUNTY 



Manganese oxide is reported to be abundant in ores of the Scott 

 (Birch Creek) mine in the Birch Creek district. 19 



A specimen of this material is a spongy, drusy mass of pyrolusite. 



Specimens sent to the National Museum by Mr. B. A. Smith, of 

 Martin, from his prospect in the Lava Creek district, 20 miles west 

 of Arco, consist of impure pyrolusite. Other specimens from the 

 same locality are wad and tourmaline. 



«• J. B. Umpleby. U. S. Oeol. Survey, Prof. Paper 97, p. 118, 1917. 



