DESCRIPTION OF VIVIANITE ENCRUSTING A FOSSIL 

 TUSK FROM GOLD PLACERS OF CLEARWATER COUNTY, 

 IDAHO. 



By Earl V. Shannon, 



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



The only locality for the ferrous phosphate, vivianite, in Idaho 

 which has heretofore been mentioned in mineralogic literature is the 

 Silver City mining district, in Owyhee County, in the southwestern 

 part of the State. The mineral occurs as crystals embedded in clay 

 in the veins of several silver mines. A large crystal from this locality 

 has been described and figured by Farrington and Tillotson. 1 The 

 purpose of the present short paper is to call attention to several 

 vivianite specimens which are now in the United States National 

 Museum (Cat. No. 87220) and which occurred under very different 

 conditions in Clearwater County in the northern part of the State. 

 These, which are broken parts of what was originally one mass, were 

 received as a gift from Messrs. Charles Brown and John Pearson, of 

 Dent, Idaho, through Mr. W. B. Compton, who writes that the ma- 

 terial was found in a gold placer mine 17 feet below the surface. 

 The extreme fragility of the specimen proves conclusively that the 

 mineral was formed in the situation where found. The largest 

 specimen, which is illustrated in Plate 93, has the form of a hollow, 

 curved, tapering cone, which is somewhat triangular in cross section 

 and is composed entirely of crusted crystals of vivianite. The gen- 

 eral shape of the object was so suggestive of that of a horn or tusk 

 that it was submitted for examination to Messrs. James W. Gidley 

 and Charles W. Gilmore, of the Division of Vertebrate Paleontology 

 in the United States National Museum, who both agree that the de- 

 posit represents the mold of a horn or tusk, but owing to the total 

 removal of all of the original material and the absence of definite 

 structure in the crystalline vivianite remaining, definite opinions 

 could not be given as to the exact character of the animal to which 

 it belonged. Mr. Gidley thinks that the original object was probably 

 the horn of a long-horned bison or the tusk of a walrus, the point 

 being too acutely tapering to be the tip of a mammoth tusk. Mr. 



» Farrington, O. C, and Tillotson, E. W., jr., Field Col. Mus. Bull., Geol. Series, vol. 3, p. 163, 1908. 



Proceedings U. S. National Museum, Vol. 59-No. 2375. 



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