DESCRIPTION OF FERROANTHOPHYLLITE, AN ORTHOR- 

 HOMBIC IRON AMPHIBOLE FROM IDAHO, WITH A NQTE 

 ON THE NOMENCLATURE OF THE ANTHOPHYLLITE 

 GROUP. 



By Earl V. Shannon, 



Assistant Curator, Department of Geology, United States National Museum. 



INTRODUCTION. 



In the summer of 1919 Mr. Frank Barker, of Kellogg, Idaho, sent 

 to the United States National Museum for identification a lot of an 

 asbestiform mineral which he had found in the Tamarack-Custer 

 mine near Gem, in the Coeur d'Alene district. This material has been 

 investigated and found to be an orthorhombic amphibole similar 

 in properties to anthophyllite but practically free from magnesium. 

 For this iron end member of the anthophyllite group the name 

 ferroantliojrfiyllite is here proposed. Requests for additional speci- 

 mens of the amphibole and associated minerals and for detailed 

 notes regarding the occurrence have elicited no reply from Mr. 

 Barker. The type material is preserved in the United States National 

 Museum (Cat. No. 93998). 



OCCURRENCE. 



The only facts regarding the occurrence of this interesting mineral 

 which are available are the statement in the letter accompanying 

 the material that it came from the mine and the fact that galena is in- 

 tergrown with the amphibole in the specimens received. The 

 latter circumstance apparently proves that the mineral occurred in the 

 ore of a galena-bearing vein. While the Tamarack-Custer mine is 

 located no great distance from the contact of an intrusive mass of 

 quartz-monzonite and several dikes of quartz-monzonite porphyry 

 are cut by the workings of the mine, the inclosing rocks are relatively 

 unaltered quartzites in which metamorphic silicates in megascopically 

 visible aggregates have nowhere been found. The occurrence of 

 considerable masses of a fibrous amphibole intergrown with galena 

 in the vein is therefore decidedly unusual. Ransome * found a 

 similar asbestiform mineral intergrown with galena in the ore of the 



1 Ransome, F. L., and Calkins, F. C, Geology and Ore Deposits of the Coeur d'Alene District, Idaho: 

 TJ. S. Geol. Survey, Prof. Paper 62, p. 99, 1908. 



Proceedings U. S. National Museum, Vol. 59-No. 2373. 



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