388 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



cite and washed free from acid was analyzed, yielding the following 

 results and ratios. In view of the fact that, owing to its fineness of 

 grain, the material is unsatisfactory for optical study, its homogenous 

 character is not entirely established. 



Analysis of benlonite {montmorillonite) from Boise County 

 (E. V. Shannon, analyst) 



Ratios 



Silica (SiOa) 



Titanium dioxide (Ti02>-- 



Alumina (AhOs) 



Ferric iron (Fe203) 



Lime (CaO) 



Magnesia (MgO) 



Barium oxide (BaO) 



Water (H 2 0) above 110° C 

 Water (H2O) below 110° C 



Total - 



JO. 956 0.191X5 0.97X5 

 .182X1 .93X1 



204X5 1.04X5 



If the bivalent bases be assumed to replace water these ratios give 

 the formula Al 2 3 .5Si0 2 .5H 2 0. In consideration of the fine grain of 

 the clay and the fact that it was not suitable for careful optical work, 

 too much discussion of the analysis is to be avoided. 



LEVERRIERITE (gouge clay) 985 



OWYHEE COUNTY 



A clay mineral, which resembles leverrierite, from the Silver City 

 district has been described under sericite. Another and much better 

 characterized leverrierite has been described from the Black Jack 

 mine in the Carson district. 89 This is a specimen (Cat. No. 24, 679, 

 U.S.N.M.) labeled "tallow-clay, Black Jack vein, Carson (Silver 

 City) district." The specimen, which has been cut into a rectangular 

 block, is smooth and resembles a hard soap. Its exterior is pale pink 

 where it has darkened on exposure, but the interior is snowy white. 

 The structure is laminated and platy, and when placed in water the 

 material softens slowly and cracks up gradually. At the end of sev- 

 eral hours immersion it had not disintegrated or swelled up in the 

 manner of bentonite. Its hardness in the specimen is about 1, and 

 when it is crushed between the teeth there is an absence of any grit. 



Under the microscope the material is transparent, colorless, and 

 entirely crystalline, with a finely foliated or felted-fibrous structure. 

 The elongation of traces of the plates is positive, so that, assuming 

 the acute bisectrix perpendicular to the plates, the mineral is optically 

 negative. The indices of refraction are a =1.488, 7=1.513. These 

 indices separate this mineral sharply from sericite and kaolinite, which 



w> In a forthcoming paper by Edgar T. Wherry this mineral is renamed beidellite. 

 •• Earl V. Shannon. Notes on the mineralogy of three gouge clays from precious metal veins. 

 U. S. Nat. Mus., vol. 62, art. 15, pp. 1-4, 1922. 



Proc. 



