S. L. P< nfi< hi- ( 'o)i>]>n.s/tion of American Monazite. 253 



chemical relations from the oxides of the cerium metals, and 

 hence should not be present as an isomorphous replacement of 

 them: and, moreover, that it is present in the above analyses 

 in very different amounts, it will seem natural, from a chemi- 

 cal point of view, to assume that the thoria, often found in 

 monazite, exists in the form of thorium silicate as an impurity. 

 A careful examination of the Portland mineral with a 

 pocket lens revealed no signs of an impurity which could be 

 identified as thorite, so that a more careful investigation was 

 made. A thin section of the mineral was examined with the 

 microscope; it showed small grains of a darker resinous sub- 

 stance scattered through the section, which are undoubtedly 

 the mechanically mixed thorite. On the fragment of Virginia 

 monazite, from which the material for analysis was obtained, a 

 very little of a resinous-looking mineral could be seen, and a 

 gment of this powdered and treated on a watch glass 

 with hydrochloric acid gave evidence of a jelly. Further, two 

 thin sections of this material were examined ; both showed 

 dark resinous particle - atvred through the section. These 

 were similar to those in the section of the Portland variety, but 

 more abundant. One of these sections was moistened with 

 hydrochloric acid, gently warmed, then carefully washed with 

 water and again examined with the microscope. White 

 blotches were seen to have taken the place of many of the res- 

 inous spots, and when a solution of fuchsin was poured over 

 the section, and the excess gently washed away, the gelatinous 

 silica retained the coloring matter. The monazite appeared 

 wholly unattacked by the treatment with hydrochloric acid. 



These observations prove beyond question the presence of 

 thorium silicate in monazite, and thus substantiate the above 

 chemical evidence. It is a curious fact that these two rare 

 minerals should be associated in this way together, and it may 

 be hoped that, with the material at our disposal in the United 

 States, good specimens of this silicate of thoria may be found. 

 A glance again at ' lal water is present in 



small quantity, as indicated' !>v the loss by ignition, and if this 

 belongs to the thorium silicate it amounts to nearly one mole- 

 cule of water to one of the silicate; this is, nearly, the propor- 



With refen 



iat phosphoi 



