THE MINERALS OF IDAHO 359 



centered optical figures suggests cleavages inclined to the principal 

 optical directions. This light product upon careful analysis, gave the 

 following results : 



Analysis of chabazite from Warm Springs Creek 



(E. V. Shannon, analyst) 



Per cent 



Silica (Si0 2 ) 45. 32 



Alumina (A1 2 3 ) 18. 84 



Liine (CaO) 9. 48 



Soda ( Na 2 0) 1. 40 



Potash (K 2 0) . 72 



Magnesia (MgO) . 44 



Water (H 2 0) above 110° C 17.80 



Water (H 2 0) below 110° C 5. 2S 



Total 99. 28 



The intermediate separation product has about the same optical 

 properties as the above except that the 7 index of some grains is 

 as high as 1.498 and there are numerous mixed grains of the zeolite 

 and the clayey material. 



The heavy separation product consists of the clayey mineral, 

 needles of thomsonite and a mineral which is clear and colorless 

 under the microscope and seems to be in rhombic grains bounded by 

 cleavages. Lying on edge these show rectangular form, parallel 

 extinction, high birefringence, and the emergence of the optic normal. 

 Lying on the broadest face they are rhombic in outline, show highly 

 inclined sweeping extinction and very low birefringence, with some 

 blue and chocolate brown low order interference colors. On this 

 face there is a rude division into sectors between crossed nicols. 

 These grains in the position to show low birefringence all show a 

 very clean cut interference figure which is biaxial positive with 2V 

 small to medium, dispersion r<v very strong. The refractive indices 

 are a= 1.505, /3= 1.507, 7=1.513. Efforts to further purify this 

 mineral with heavy solutions were not successful, as the thomsonite 

 and a part of the clayey material had had about the same specific 

 gravity. Treated with hydrochloric acid at boiling it is slowly 

 decomposed leaving a silica skeleton. It is not at all certain whether 

 this last described mineral is a variety of the chabazite or some other 

 zeolite, such as, for example, heulandite. 



ELMORE COUNTY 



A specimen labeled as from Snake River lava, 5 miles below 

 Glenns Ferry, Elmore County, consists of a vesicular lava contain- 

 ing considerable amounts of a crystalline white zeolite associated 

 with a little thomsonite, overlying amber calcite. Numerous partial 

 crystals or fragments were examined, some of which apparently 

 were simple chabazite rhombohedra, while others had the appearance 



