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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 41 . 



variscite with phosphosiderite (2) and their greater difference from 

 the values of the other minerals. 



Comparison of axial ratios (first orientation). 



It is to be particularly noted that the agreement of values is much 

 closer for variscite and phosphosiderite (second position) than for 

 variscite and scorodite or strengite. Tliis fact led to the suggestion 

 that perhaps the mineral here described was not variscite but a new 

 mineral bearing the same relation to true variscite that phosphosider- 

 ite is supposed to bear to strengite. The analysis, however, shows 

 that the crystallized variscite from Utah agrees well with the formula 

 AI2O3.P2O5.4H2O. A careful study of the relations of phosphosiderite 

 to strengite, considered with the close crystallograpliic values of 

 phosphosiderite and variscite, lead to the conclusion that phospho- 

 siderite and strengite are identical notwithstanding the apparent 

 differences in the optical properties. 



SECOND ORIENTATION. 



In the second possible orientation the large face is made the macro- 

 pinacoid a (100). As the optical axial plane of variscite is parallel 

 to this large face, such an orientation would bring variscite into optical 

 conformity with scorodite and strengite. It then becomes necessary, 

 however, in order to retain the crystallographical analogy, to give to 

 the prism m the symbol (340). The dome e then becomes (102) and 

 the close angular agreement of the minerals in this position can be 

 seen by the following table: 



Comparison of angles (second orientation). 



