288 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



SHOSHONE COUNTY 



The material described as ferroanthophyllite was collected in 

 the Tamarack and Custer mine on Ninemile in the Coeur d'Alene 

 district by Frank Barker who sent it to the United States National 

 Museum for identification. The mineral contains galena and is 

 stated to have occurred in the ore. While this mine is located no 

 very great distance from the contact of an instrusive mass of quartz 

 monzonite and several dikes of quartz-monzonite porphyry are 

 reported to have been encountered in the mine workings, the inclos- 

 ing rocks are unaltered quartzites in which metamorphic silicates 

 in megascopically visible aggregates have not heretofore been re- 

 ported. The occurrence of considerable amounts of this amphibole 

 in the vein is therefore decidedly unusual. Inquiries and requests 

 for additional specimens have been directed to both Mr. Barker and 

 to the mining company but have not been answered. 



The material as received consists of splintery-fibrous masses of 

 a pale grayish-green color when dry and olive-green when moist. 

 In all about 250 grams of the material were received in broken pieces. 

 The individual fibrous masses reach a maximum length of 6 cm. 

 The material separates easily into fine silky fibers which are mod- 

 erately strong and flexible, being comparable to a poor quality of 

 chrysotile, which the mineral resembles. The only associated 

 mineral is a little fine granular galena which occurs interstitially 

 between the fibers, as small nodules around which the fibers are 

 curved or as fillings of small fractures in the mineral. 



Under the microscope the mineral is in the form of very thin fibers 

 which show positive elongation and parallel extinction. The indices 

 of refraction determined are a =1.668, 7=1.685, birefringence 

 0.017. Singly the fibers are colorless but thick aggregates of fibers 

 are colored and pleochroic, X = pale brownish green, Z = deep brown- 

 ish green. 



An analysis made upon selected fibrous material gave the following 



results : 



Analysis of ferroanthophyllite 



(E. V. Shannon, analyst) 



Per cent. 



Silica (Si0 2 ) 49.30 



Alumina (A1 2 3 ) 1. 30 



Ferric oxide (Fe 2 3 ) 2. 15 



Ferrous oxide (FeO) 30. 50 



Manganous oxide (MnO) 3. 48 



Lime (CaO) 10. 73 



Magnesia (MgO) - . 66 



Water (H 2 0) above 110° C 2. 13 



Water (H 2 0) below 110° C . IS 



Total 100. 43 



