REPORT OF THE DIRECTOR I917 179 



such as cronstedite, thuringite, delessite, and its closest affinity seems 

 to be with the chamosite variety of thuringite --that is, the variety 

 rich in ferrous iron and poor in ferric iron. 



Zalinski, 1 with much reason, regards chamosite as a distinct 

 species, but whether or not this conclusion is finally accepted 

 is unimportant in the present connection. His analyses, shown 

 averaged and recalculated to ioo in no. 3, were made on carefully 

 separated material and with a purely mineralogical end in view, 

 while Doctor Morley's analyses were made to show the nature of 

 the rock as a whole, as well as that of the particular mineral in ques- 

 tion, and considerable lack of agreement is inevitable. 



But, in view of this essential difference in the nature of the data, 

 as well as the peculiar and variable character of the minerals con- 

 cerned, the divergence of results is no more than would be expected. 

 As a matter of fact, the results of the present analyses agree better 

 with Zalinski's analyses of chamosite than do the latter with most 

 analyses of thuringite (illustrated by no. 6) of which mineral chamo- 

 site is generally considered a variety. 



From the analytical results given above, Zalinski derives the 

 formula H 6 (FeMg) 3 Al 2 Si 2 0i 3 , while for thuringite, he derives the 

 formula H 18 (FeMg) 8 (AlFe) 8 Si 6 4 i. 



The ferrous silicate m gives the following molecular equivalents, 

 AI2O3 being taken as 1 in. the second column: 



Si0. 2 -439 i-87 



A1.0, • - 2 34 IO ° 



FeO \ 706 3 . 00 



MgO J 



H 2 -7Q5 3-QQ 



While the silica ratio is low, the evidence points toward the same 

 formula as that obtained by Zalinski. 



In the case of the ferrous silicate 2a, the corresponding figures are: 



c; , -4i6 I -77 



1&;:;::::::::::::::::::.. , -^ 



FeO .738 3- H 



MeO > 



H?0.'.7. -4JO 1-95 



The ratios here are even less satisfactory than in the preceding 

 case, but, so far as they may be trusted, they indicate the same form- 

 ula, with one less molecule of water, or H 4 (FeMg)3Si 2 0i2. 



1 Zalinski, E. R., Untersuchungen iiber Thuringit u. Chamosit aus Thuringen u. 

 Umgebung: Neues Jahrb. f. Min. etc., B. B. XIX, p. 40-84, 1904- 



