RockfTom the Highwood Mountains of Montana. 319 



Zeolitization and a prohahle new zeolite. — The small portion 

 of powder which was left floating in the heavy solution after 

 the precipitation of the leucite at 2*405 was found to come 

 down gradually as the speciiic gravity was lowered. At 2 '357 

 much had already fallen. At 2*30 a small portion was still 

 floating, and this was then thrown down and analyzed, in the 

 hope of learning what the character of the zeolitization 

 mentioned above had been. Examined under the microscope 

 it was found to consist of isotropic grains, presumably analcite, 

 mingled with a substance of low birefraction. The amount of 

 material was less than -4 gram, and of this one-tenth gram was 

 taken for the determination of water. 



The analysis (by L. Y. Pirsson) gave the following results : 



Ratios. A. B. 



SiO, 50-18 -836 -836 4 3-46 



Al.Og 25-07 -243 -243 Li6 1 



Fe.Og trace 



CaO 1-YO -030 ) 



Na,0 6-53 -105 V "224 1-06 '93 



K^O 8-36 -088 ) 



H^O 9-02 -501 -501 2-39 2-06 



Total 100-86 



The substance dissolved readily in acid with separation of 

 gelatinous silica. The ordinary analytical errors are of course 

 somewhat magnified by the small quantities operated upon, but 

 as great care was taken it is not believed they are sufficient to 

 affect the ratios. In the first column under A one-quarter of 

 the silica is taken as unity, under B the alumina is taken as 

 unity. It will be seen that the ratio of the protoxides to the 

 sesquioxide to the water is 1 : 1 : 2, as demanded by the anal- 

 cite formula, but that there is a deficiency of silica. The 

 microscope having already shown that two substances are pres- 

 ent, one of them isotropic and most probably analcite, if we 

 consider the soda present as forming that mineral and deduct 

 sufficient silica, water and alumina to make with it analcite, 

 the remainder reduced to 100 becomes : 





Found. 



Ratios 



. 





Calculated 



SiO,._.. 



45-85 



•764 



•764 



3-01 



3 44-6 



Al,03... 



2G-07 



•253 



•253 



1 



1 25^6 



CaO. .. 

 K,0.... 



3-12 



15-35 



•056 1 

 •162 \ 



•218 



•86 



1 ^'^ 

 ' 17^5 



H,0.... 



9-61 



•534 



•534 



2-11 



2 8^9 



100^00 lOO^O 



\ 



