266 Prof. J. P. Cooke on the Vermiculites. 



yellow variety, mean of two determinations, 2*402. Before the 

 blowpipe, fuses with difficulty to a brown enamel. The following 

 analyses were made by Mr. C. E. Munroe, assistant in the labo- 

 ratory of Harvard College : — 



Green variety ofHallite. 





Si. 



Al. Fe. 



Fe. 



Mg. 



K. 



H. 





(1) . 



35-97 



7-61 8-83 



1-13 



31-34 



0-43 



14-32 = 



=99-63 



(2) . 



35-80 



7-29 8-73 



1-13 



31-56 



0-49 



14-33 = 



= 99-33 



Mean. 



35-89 



7-45 8-78 



113 



31-45 



0-46 



14-33 = 



= 99-49 





19-14 

 19-14 



3-47 2-63 



v v ) 



6-10 



0-25 



12-58 



0-08 



12-74 

 12-74 









12-91 









3 



0-96 





2-02 





2 







3 



1 





2 





2 









Yellow variety of Hallite. 









Si. 



Al Fe. 



Fe. 



Mg. 



e. 



H. 





(1) • 



35-17 



7-74 9-76 



0-32 



31-61 



0-56 



14-65 = 



=99-81 



(2) . 



35-34 



7*42 9-61 



0-32 



3L-41 



0-65 



14-91 = 



= 99-66 



Mean. 



35-26 



7*58 9-68 



032 



31-51 



0-61 



L4-78 = 



=99-74* 





18-81 

 18-81 



3-53 2-90 



v J 



6-43 



o-io 



12-60 



0-10 



13-14 

 13-14 









12-80 









3 



1-03 





2-04 





2-09 







3 



1 





2 





2 





It will be seen from the above analyses that, although the 

 atomic ratio between all the basic radicals and the silicon is the 

 same as in Culsageeite, Jefferisite, and Biotite, the ratio between 

 the protoxide and sesquioxide radicals is very different. In this 

 respect the mineral resembles the phlogopite micas, in which 

 also the protoxide radicals preponderate ; and the symbol given 

 above for Hallite, less the water, is identical with that given by 

 Professor Dana as the more probable formula of the phlogopites. 



The opacity produced by the interspersed material made it 

 difficult to determine the optical characters of the mineral, as 

 the rings produced with polarized light could only be seen with 

 very thin plates, and the cross was therefore ill denned ; so that, 

 although in some cases there appeared to be a separation of the 

 hyperbolas, the plates could not be distinguished from uniaxial. 

 On one specimen the hexagonal form was very perfect, and the 

 crystal presented the planes of a rhombohedron having an angle 

 * Trace of man sane se. 



