390 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



HALLOYSITE (493) 



Hydrous aluminium silicate, Amorphous 



Al 2 3 .2Si0 2 .2H 2 0-f-nH 2 0. 



Halloysite is a clay mineral, corresponding to the crystalline 

 kaolinite in composition, which is amorphous and isotropic under 

 the microscope. It is probably a fairly common mineral in Idaho, 

 but few specimens of the clays have been examined microscopically 

 and it has been identified only from one locality, as follows: 



BANNOCK COUNTY 



A specimen of a clayey mineral sent to the National Museum 

 for identification from Pocatello, Bannock County, is largely com- 

 posed of an isotropic clay mineral which is doubtless halloysite. 

 The material is stated to occur in large amount near Pocatello. 

 The sample, dry, as received, is slightly creamy white in color and 

 is very light and rather tough. When cut or rubbed it assumes the 

 usual soapy luster. Upon being thrown into water or moistened it 

 very energetically disintegrates into a sandy material which is 

 not plastic. The clay adheres to the tongue and has a strong clayey 

 odor. 



Upon being heated for 1 hour at 110° C. the material reached 

 a constant weight with a loss of 12.86 per cent of water. Ignition 

 to a full red heat resulted in the loss of an additional 9.62 per cent. 

 A sample which had been dried at 110° C. gained 3.14 per cent 

 of the original weight in 20 minutes in air and upon standing over- 

 night in air regained all of the water lost at 110°. The mineral, 

 dried at 110° C, and examined microscopically is very cloudy until 

 it soaks up the oil. It is isotropic with and index of 1.550 to 1.552. 

 It contains about 6 per cent of birefracting material, having the ap- 

 pearance of feldspar which shows albite twinning and has a maximum 

 index of refraction of 1.54. This is doubtless albite. 



URANOPHANE (503) 



Hydrous uranium-calcium silicate, Orthorhombic. 



Ca0.2U0 3 .2Si0 2 .6H 2 0. 



BOISE COUNTY 



The yellow uranium mineral, uranophane, is reported to occur 

 in Boise County at Centerville in the Idaho Basin. 1 The source 

 of this report has not been ascertained and no further confirmation 

 has been received. Inasmuch as monazite, columbite, samarskite, 

 polycrase, and other minerals characteristic of rare earth bearing 

 pegmatites occur in this vicinity, the occurrence of uranophane is to 

 be expected. 



i U. S. Geological Survey, Bull. 624, p. 121, 1917. 



