THE MINERALS OF IDAHO 



389 



have higher indices. The material compares, in refractive indicts. 

 with the lowest set of values given by Larsen for leverrierite. 



Heated in the closed tube the clay yields abundant neutral water 

 at a very moderate temperature. In the forceps it decrepitates 

 mildly and fuses with moderate ease on thin edges to a white blebby 

 enamel, the fused portion becoming markedly incandescent. Mate- 

 rial which had been proven free from contamination by optical study 

 was available in quantity for analysis, and the analysis was carefully 

 made on ample material. The loss of water at 110° C. was found 

 to be 14.48 per cent, the mineral reaching constant weight at this 

 temperature with 2 hours heating. The first hour the loss was 14.28 

 per cent. During the second hour additional loss of 0.20 per cent 

 was sustained, while several hours additional heating occasioned no 

 further loss. When exposed again to the air of the room, however, 

 the material proved to be very hygroscopic, and a sample which had 

 been dried to constant weight at 110° C. regained all of its original 

 water content upon standing overnight in the air of the room. A 

 similarly dehydrated sample regained 2.18 per cent of its original 

 weight upon standing overnight in a desiccator over calcium chloride. 

 Samples dehydrated at 110° C. and allowed to stand overnight over 

 sulphuric acid show a gain of several per cent ; following which th ex- 

 can not again be brought back to the original dry weight at this 

 temperature. The analysis gave the following results and ratios: 



Analysis and ratios of leverrierite, Black Jack vein 



Silica (Si0 2 ) --- 



Alumina (AI2O3) 



Ferric iron (Fe203) 



Lime (CaO) 



Magnesia (MgO) 



Potash (K2O) 



Soda (Na 2 0) 



Water (HjO) above 110° C 

 Water (H2O) below 110° C 



Ratios 



0.752 0.752 0.251X3 1.00X3 

 ;^| .27(1 .270X1 1.10X1 

 '. 049 1 



"oof - 056 - 28() X5 ' 

 .002J 



.804J 



.056 .280Xe 1. 12Xf 

 a o 



1.257 .251X5 1.00X5 



These ratios yield the formula. - RO.R 2 2 .3Si0 2 .5H 2 0, which may 



be expanded to EO. 5AL,0 :j .15Si0 2 .25H 2 0. Assuming the miscella- 

 neous bases to replace water, the formula obtained is simply A1 2 3 . 

 3Si0 2 .5H 2 0. 



Other similar clays occurring in these silver veins as gouges may 

 likewise be leverrierites, but Lindgren's published determinations on 

 many of them made by Hillebrand, as mentioned above under sericite 

 and kaolinite, show too little low temperature water to be leverrierite. 



