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BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



lina, which are .more cheaply mined, and the Idaho localities can not 

 successfully compete in the limited market. The potential commer- 

 cial value of the Idaho deposits is dependent upon the development 

 of uses, which will create a market demand for the cerium metals 

 which are the essential constituents of monazite. With the rapid 

 advances of chemical and metallurgical industry this event will 

 probably occur at no very distant date. 



The work of the several geologists who have examined the Idaho 

 monazite-bearing area seems to indicate that the monazite is an orig- 

 inal mineral present as an accessory constituent of the granitic 

 rock of the great central Idaho batholith. Lindgren panned crys- 



Fios. 128-130.— Monazite crystals from placer concentrates. Boise County 



tals of both monazite and zircon from angular granite soil formed 

 by the disintegration of the granite on slopes where these minerals 

 could have no other source. The nature of the mineral, monazite, 

 its occurrence elsewhere throughout the world, and the fact that it 

 is not invariably present in drainage basins in the granitic area 

 probably indicate that it occurs, not in the normal granite, but in 

 the small coarsened pegmatitic streaks and veins which are locally 

 abundant in the granitic mass. 



The description of the monazite from the localities in Boise County 

 will suffice for that from all of the other places where this mineral 

 has been found in the State since they present no essential differ- 

 ences. In color it is commonly resinous golden-yellow to amber 

 or orange brown. Only a few crystals were found which had what 



