THE MINERALS OF IDAHO 427 



clinographic projections, a hypothetical untwinned crystal of the 



mineral. 



VIVIANITE (597) 



Hydrous iron phosphate, 3FeO.P 2 5 .8H 2 0. Monoclinic. 



Vivianite has been noted in specimens from three localities in 

 as many counties in Idaho, described as follows : 



CLEARWATER COUNTY 



A paper has previously been published calling attention to several 

 vivianite specimens which are from Clearwater County 30 and are 

 now in the National Museum (Cat. No. 87220, U.S.N.M.). These 

 which are broken parts of what was originally one mass were 

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

 Idaho, through W. B. Compton, who writes that the material 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 18, 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 general shape of the 

 object was so suggestive of that of a horn or tusk that it was sub- 

 mitted for examination to James W. Gidley and Charles W. Gilmore 

 of the Division of Vertebrate Paleontology in the United States 

 National Museum, who both agree that the deposit 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 crystal- 

 line 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. Gilmore, however, 

 has pointed out a tendency of tusks of the mammoth to develope a 

 cone-in-cone structure and to separate, upon weathering, into a 

 succession of horn-shaped segments having much the form of the 

 interior cavity of the vivianite specimen. On chemical grounds it 

 is apparent that the tip portion of a horn of this length, owing to 

 its low content of mineral matter, would scarce supply the amount 

 of phosphoric acid represented by the vivianite. 



The exterior of the specimen, as shown in the photograph, is made 

 up of masses of vivianite crystals. The crystals are grown outward 

 from a thin platy layer which, while also consisting of vivianite, 

 apparently outlines the original object and has a remotely fibrous 



m Earl V. Shannon. Description of vivianite incrusting a fossil tusk from gold placers of Clearwater 

 County, Idaho. Proc. U. S. Nat. Mus., vol. 59, pp. 415-417, 1921. 



