410 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



EUXENITE (534) 



Columbate and titanate of yttrium, Orthorhombic. 



erbium, cerium, and uranium. For- 

 mula doubtful. 



CUSTER COUNTY 



Euxenite lias been reported to occur in heavy black rolled pebbles 

 and masses devoid of cleavage or crystal outline in gold-bearing 

 gravels at the head of Kelly Gulch on a claim which is only 300 feet 

 from the low divide between Kelly Gulch and Stanly Basin. The 

 mineral, which is strongly radioactive, has not been quantitatively 

 analyzed. 16 The locality is the same as that which furnished bran- 

 nerite and the so-called euxenite may have been brannerite. 



POLYCRASE (535) 



Columbate and titanate of yttrium, 

 erbium, cerium, and uranium. For- Orthorhombic. 



mula doubtful. 



BOISE COUNTY 



A sample of " oversize" coarse sand from a placer concentrate from 

 Centerville contains abundant grains and rough crystals of a dark 

 brownish or greenish-black mineral not very dif- 

 ferent in appearance from the samarskite. The 

 crystals, which reach 1 cm. in diameter, are or- 

 thorhombic in aspect and vary from square- 

 prismatic to thin tabular. They are all coated 

 with a thin exterior crust of a pale-yellow altera- 

 tion product. Within this shell the crystals and 

 grains consist of a brownish-black glassy ma- 

 terial having a conchoidal fracture and a brown 

 streak. Under the microscope the fragments are 

 transparent, isotropic, and brown in color. The 

 from black sand, mineral is intensely radioactive. Several lots of 

 Idaho city, Boise ^ material have been received and it seems to be 



COUNTT 



common, especially in the Poncia placer tract. A 

 lot of the fragments of the mineral are shown in natural size in Plate 

 15, while in Plate 16 is shown a radioactivity photograph made from 

 the same lot of pieces. F. L. Hess has turned a rather large sample 

 of this mineral over to the Museum for investigation which has not 

 yet been undertaken. The properties and appearance of the mineral 

 are identical in most respects with the polycrase of Marietta County, 

 N. C, and for the present it will be referred to that mineral. This 

 mineral, recognizable by its light-colored coating, occurs sparingly 

 also in the samarskite and columbite-bearing concentrates from 

 Idaho City. A crystal from this lot gave measurements on the 



'« Robert N. Bell. 16th Ann. Rept. Mining Industry of Idaho for 1914, p. 29. 



