MORDENITE AND ASSOCIATED MINERALS FROM NEAR 

 CHALLIS, CUSTER COUNTY, IDAHO. 



By Clarence S. Ross, 



Geologist, United States Geological Survey, 



AND 



Earl V. Shannon, 



Assistant Curator of Geology, United States National Museum. 



INTRODUCTION. 



In 1917 Mr. Milton A. Brown, of Challjs, Idaho, sent a specimen 

 of a very fine cottony mineral of snow white color to the United 

 States National Museum for identification. This mineral, which was 

 thought to be asbestus, was said to be available in considerable 

 quantity. Upon examination in the Museum laboratory this was 

 found to be a fibrous zeolite, and optical examinations by Wherry 

 and Larsen showed it to have properties similar to those of the 

 rare mineral ptilolite. Chemical examination by Koch supported 

 this conclusion, although the mineral was so mixed with small 

 grains of quartz that it was not suitable for analysis. A short note 

 on the occurrence was published by Koch.^ 



In 1921 a box of some 50 pounds of specimens of the zeolite and 

 associated minerals from this locality was received at theMusemn. 

 This material has been subjected to a detailed examination, the 

 results of which are here presented. 



NOMENCLATURE. 



Dr. Waldemar T. Schaller has recently critically reviewed the 

 group of zeolites which includes mordenite, ptilolite, and flokite. 

 In addition to the existing literature, which includes recent work 

 by Walker and Boggild, Schaller has considered new analyses made 

 by himself and the analytical data presented below together with 

 numerous new optical determinations. One of the results of this 

 admirable work was to show that the Idaho mineral here considered 

 is not ptilolite, as at first supposed, but is, in reality, mordenite.^ 



1 Louis A. Koch. A new occurrence of ptilolite. American Mineralogist, vol. 2, p. 143, 1917. 

 * Waldemar T. Schaller. Unpublished paper presented before the first meeting of the Mineralogical 

 Society of Washington, February, 1923. See abstract in Amer. Mineralogist, vol. 8, p. 93, 1923. 



No. 2509. — Proceedings U. S. National Museum, Vol. 64. Art. 19. 



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