416 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



COLLOPHANITE (549a) 



PHOSPHORITE, PHOSPHATE ROCK 



Calcium phosphate, Amorphous. 



9Ca0.3P 2 5 .CaO.C02.H 2 + nH 2 0. 



Collophanite is the mineral which makes up the phosphoric acid- 

 bearing portion of the phosphorite or rock phosphate which occurs 

 in all of the southeastern counties of Idaho and adjoining counties 

 of Wyoming and Utah in very great amount. This area probably 

 constitutes the largest reserve of high-grade rock phosphate in the 

 world, and much of the land is now in Federal phosphate reserve. 

 While not of especial interest from the mineralogical viewpoint, 

 these deposits are of great practical importance as such phosphate 

 rocks are used in the manufacture of soluble phosphates which are 

 essential to plant growth and which must be used in the fertilization 

 of agricultural lands. The phosphorite deposits have been thor- 

 oughly investigated by the United States Geological Survey and for 

 detailed descriptions of the field the reader is referred to the several 

 publications on the subject by G. R. Mansfield and others. 22 The 

 following description is copied from one of these reports. 



The phosphorite is characterized by an oolitic texture which may 

 be lacking where the grain of the rock has been destroyed by pressure 

 or shearing. The ovules are rounded grains built up in roughly 

 concentric structure and range in size from extremely minute specks 

 to bodies a centimeter or more in diameter. Many of them are 

 irregularly flattened as though worn by attrition. The ovules are 

 in general darker than the matrix and many of them have a shiny 

 black coating like desert varnish. 



When fresh the rock is dark brown to almost black in color, but 

 that which has weathered is light bluish-gray. The rock which 

 has lost its oolitic texture through metamorphism or pressure does 

 not turn light upon weathering. The phosphate rock and associated 

 limestone emit a strong bituminous-fetid odor when struck. 



The rock-phosphate deposits are original sedimentary formations 

 laid down at the time that part of the earth's surface was largely 

 covered with water. Since the time in which the phosphatic strata 

 were deposited other sediments have been accumulated, so that 



» F. B. Weeks and W. F. Ferrier. Phosphate deposits in western United States. U. S. Geol. Survey, 

 Bull. 340, pp. 441-447, 1908. 



R. W. Richards and G. R. Mansfield. Preliminary report on a portion of the Idaho phosphate reserve- 

 U. S. Geol. Survey, Bull. 470, pp. 371-440, 1911. 



Hoyt S. Gale and R. W. Richards. Phosphate deposits in Idaho, Wyoming, and Utah. U. S. Geol. 

 Survey, Bull. 430, pp. 457-535, 1910. 



R. W. Richards and G. R. Mansfield. Geology of the phosphate deposits northeast of Georgetown, 

 Idaho. U. S. Geol. Survey, Bull. 577, 1914. 



A. R. Schultz and R. W. Richards. A geological reconnaissance in southeastern Idaho. U. S. Geol- 

 Survey, Bull. 530, pp. 267-284, 1913. 



