210 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



LEMHI COUNTY 



In Lemhi County limonite in the usual forms is abundant in almost 

 every district. Waxy amorphous limonite has been noted in speci- 

 mens from the Creek tunnel on Patterson Creek. In the Texas 

 district limonite in ocherous form is abundantly mixed with cerusite 

 in the lead ores. A specimen from the Oriole lower tunnel on the 

 north side of Liberty Gulch contains abundant small and perfect 

 pyritohedral pseudomorphs of limonite after pyrite in a gangue of 

 calcite and ocherous limonite. Another specimen from the Copper 

 Queen mine, McDevitt district, likewise shows pyritohedral pseudo- 

 morphs of limonite after pyrite. 



SHOSHONE COUNTY 



Limonite is very common in the oxidized portions of the lead-silver 

 deposits of the Coeur d'Alene mining district. Great craggy masses 

 which mark the outcrops of many veins consist of fragments of 

 quartzite cemented by limonite, and this mineral is abundant in the 

 surface cuts of nearly all mines. It occurred both as hard and 

 compact jaspery material, as soft ocherous masses, and as cellular 

 or spongy dark velvety brown masses in the oxidized ores associated 

 with much cerusite. This limonite has to some extent been derived 

 from pyrite, but its most abundant source has been the siderite which 

 is the principal gangue mineral of the deposits. As the gangue 

 siderite is somewhat manganiferous, much of the limonite is also 

 manganiferous. The Evolution vein near Osburn contains a wide 

 filling of ferrugineous calcite and, where this has oxidized, large 

 amounts of limonite remain behind. Large masses of limonite 

 result from the alteration of ankerite and siderite veins south and 

 east of Mullan. 



The mine waters of the Bunker Hill mine contain much iron in 

 solution in the form of the bicarbonate. Where these waters drip 

 into abandoned workings the iron becomes oxidized by contact with 

 the air and is precipitated as a slimy ooze of limonite on the sides 

 and floors or hardens into stalactites of limonite which hang from the 

 roof. 



PSILOMELANE (269) 



Hydrous manganese oxide, formula Amorphous, 



doubtful, possibly a hydrated col- 

 loidal mixture of MnO and Mn0 2 . 



Psilomelane is probably the commonest of the manganese oxide 

 minerals, and for this reason all occurrences of black oxide manga- 

 nese minerals not sufficiently well characterized to be definitely 

 referred to pyrolusite or some other more definite species are men- 

 tioned under this name. Numerous minor occurrences are known 

 of which a few typical localities are mentioned. 



