604 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



stamp mills, while the gritty particles fell to the bottom. By pouring off the sus- 

 pended matter, allowing to settle, decanting the supernatant liquid, and drying the 

 slimy deposit, an apparently pure matter was obtained, showing the pearly luster of 

 the original mass, and containing, like that, when air dried, about one-quarter of 1 

 per cent, of hygroscopic moisture. This is not included in the above analysis. No 

 further loss occurred on prolonged heating until a temperature considerably above 

 100 C. was reached, while a strong red heat was requisite for complete expulsion of 

 the water. 



No altogether satisfactory formula can be deduced from the figures in the table. 

 On dividing the molecular value by that for water, as being most accurately deter- 

 mined, the ratio is found to be 



SiO 2 : A1 2 O 3 : Rj(R)O : H 2 O 



9.93 4.09 1.87 3.00 

 or, approximately, 



10 : 4 : 2 : 3. 



As no other specimens of a similar nature, from the Amie or other mines, have 

 been observed, by analysis of which it could be ascertained whether the above ratio 

 remains constant or not, it would be rash to affirm that the material analyzed repre- 

 sents a distinct mineral species, the final product of the alteration of the porphyry 

 from which it is derived. 



No. 2, pure white, veined with maugane.se dioxide ; compact, hardness about 2, 

 rubbing off on the fingers when dry. When fresh and moist, frequently greenish in 

 color, opaline in appearance, and semi-transparent, especially on the thin edges, becom- 

 ing opaque on exposure. Insoluble in hydrochloric acid. Portions free from MuO 2 

 taken for analysis. 



It was found that after two or three years' exposure to the air a large amount 

 of water, 3.36 per cent, of that given in the analysis, was still retained in a very weak 

 state of combination, apparently as hygroscopic moisture, since it escaped over sul- 

 phuric acid. No further loss occurred ou heating at 100 C., nor below 160 C. to 170 

 C., although blackening took place, due to carbonization of organic matter. Dried 

 over sulphuric acid or at 100 C., the powder was so extremely hygroscopic that it was 

 deemed advisable to make the analysis upon air dried material. The percentage of 

 loosely combined or hygroscopic water was found to decrease slowly ou long exposure 

 of lumps to the air, so slowly as to be perceptible only at intervals of a month or more. 

 Deducting all water driven off at 100 C., the molecular ratio SiO z : A1 Z O 3 : H 2 O is 

 1.98 : 1.00 : 2.20, thus showing the substance to be closely allied to kaoliuite. 1 



Nos. 3, 4, and 5. In general appearance 4 and 5 differ little from the substance 

 last described. Color, white, streaked frequently with iron and manganese oxides; 

 hardness, after long exposure, in case of 5, about 2. Practically insoluble in hydro- 

 chloric acid. No. 3 is pure white, and resembles 1 ; it contained no hygroscopic water. 

 No. 4 contained but 1.23 per cent. ; while No. 5 retained 4.58 per cent, of the same 

 (included in the analysis), after long exposure to the air in the form of lumps. 



'The same is fonnd in the Morning Star consolidated group of mines according to L. D. Ricketts, 

 one of whose published analyses (The Ores of Leadville, Princeton, 1883) shows a ratio SiO 2 : Al 2 Oj : 

 H 2 O = 2 : 1:3, probably including hygroscopic or weakly combined water. 



