Weidman and Zenker — Marignacite. 291 



discussion. As already stated, the pyrochlore is associated in 

 the rock with quartz, feldspar and varieties of aluminous 

 acmite containing 5 per cent A1 2 3 and above, and these min- 

 erals to a slight extent were necessarily included in the pow- 

 dered material prepared for the specific gravity separation. 

 Previous to powdering the material, however, each pyrochlore 

 crystal was examined and all material clinging to the latter was 

 rubbed off so far as possible. The relatively high specitic grav- 

 ity of the pyrochlore, namely 4*13 as compared with 2*6 of quartz, 

 2 - 6 of feldspar, and 3*5 of acmite, should furnish a favorable 

 means for separation by the method adopted. The fact that 

 the chemical analysis shows only a trace of alumina indicates 

 the essential absence of feldspar and aluminous pyroxene in 

 the material analyzed. And if these minerals were success- 

 fully removed from the powdered material in the process of 

 separation by the specific gravity method, it seems reasonable 

 to believe also, that the quartz was removed at the same time 

 and to the same extent. Hence it seems probable that the 

 silica is a normal constituent of this mineral. 



If the Si0 2 is an original constituent of this pyrochlore, it 

 differs in this respect from other varieties of pyrochlore. 

 Silica is shown in the analysis of some of the members of the, 

 columbate-tantalate groups,' but it is usually considered" of 

 secondary origin. However, if the silica with the titanium 

 oxide are normal constituents, they indicate an interesting 

 relation in the composition of this pyrochlore to many of 

 the titano-silicate minerals, such as tscheffkinite, johnstrupite, 

 mosandrite, rinkite and also to dysanalyte. In content of 

 cerium oxide this pyrochlore from Wausau is higher than in 

 any of the other pyrochlores and in its high content of cerium 

 oxide it also resembles the titano-silicates referred to. This 

 pyrochlore with appreciable content of Si0 2 , believed to be a 

 normal constituent, therefore, shows an interesting relation in. 

 composition between the titano-silicates on the one hand and 

 of the columbate-tantalates on the other. 



In the table the analysis of the pyrochlore from Wausau is 

 shown in comparison with the analyses of the typical varieties 

 described by various investigators. By comparison of the sev- 

 eral analyses in the table it may be seen that the pyrochlore 

 from Wausau differs from the others in the proportion of each 

 of the several acid and basic radicals. The principal difference 

 in composition with respect to individual constituents appears 

 to be the relatively higher content in the Wausau pyrochlore 

 of cerium and yttrium, and the lower content of lime and iron 

 as compared with the other members of the pyrochlore group. 

 The presence of silica in the Wausau pyrochlore is also a dis- 

 tinctive feature, as already stated. 



