Geology and Mineralogy. 223 



Analc. iEg.-aug. Neph. San. Mel. Ti. Hem. Cal. H 2 

 71-0 14-0 5-0 40 10 0-5 1-0 20 15 = 100*0 



A chemical analysis of this type by M. F. Connor gave : 



Si0 2 Ti0 2 A1 2 3 Fe 2 3 FeO MnO MgO CaO Na 2 K 2 H 2 CO a Total. 

 54-04 0-20 1886 3-30 076 0-08 0-70 2-32 977 226 7-00 0-80=10009 



The specific gravity is 2-39. The other varieties differ chiefly in 

 the amount of analcite, texture, etc. The author appears to hold 

 with Knight that the analcite is primary, as shown by its crystal 

 form and association with unaltered orthoclase and nephelite. 



From the descriptions given by the two authors cited it seems 

 not altogether certain that the analcite is primary ; if it is so, 

 this is a most surprising occurrence of an igneous rock. Hitherto 

 it has been considered that the habitat of primary analcite was 

 in the intrusive rocks where the pressure would tend to restrain 

 the escape of the water vapor and force it to take part in the 

 crystallization ; here, however, it would appear to have been 

 formed in the lavas undergoing explosion. If primary, the lava 

 might be considered the effusive form of the analcite-syenite 

 described by Tyrrell from Ayrshire, Scotland (Geol. Mag., vol. 

 ix, p. 70, 1912), except that the latter contains much more felds- 

 par ; had the blairmorite crystallized anhydrously it would have 

 formed chiefly albite and nephelite, a mariupolite. 



The doubt concerning the primary nature of the analcite arises 

 from the conclusion of the investigators that these pyroclastics 

 were laid down in sea-water. If so, their original heat would 

 have caused them for a long time to have been digesting in warm 

 solutions of sodium salts, under which circumstances Lemberg's 

 experiments show that leucite is converted into analcite. Whether 

 under these conditions the feldspars would have also been attacked 

 is less certain. The question thus arises whether the lavas may 

 not have been originally leucitic ? l. v. p. 



5. On the Mineral Empressite ; by W. M. Bradley. (Com- 

 municated.) — In the number of this Journal for August, 1914 

 (p. 163) there was given a discussion and analyses of a silver-tel- 

 lurium mineral known as empressite. A letter recently received 

 from Mr. E. J. Dittus of the Colorado School of Mines contained 

 the results of his analyses of a silver-tellurium mineral which 

 was donated to the Geological Department of the Colorado 

 School of Mines, by Mr. Frank Leavitt of Bonanza, from the 

 Kerber Creek District, Colo. The analyses which follow show 

 exceptionally close agreement to those given for empressite and 

 help to confirm the conclusion that the formula of empressite is 

 AgTe : 



I II Ave. Mol. ratios 



Insoluble 0'32 0-34 0-335 



Ag 43-71 43-68 43*695 0'40503 



Te 53-86 53-81 53'835 0*43710 



Fe 2-17 2-16 2-165 0-03800 



CaO . _ _ trace trace trace 



Ag : Te= 1: 1-08 



Total 100-06 99-99 100*03 



