474 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



analyses of prochlorite. Computing the molecular ratios from the 

 above analysis, however, leads to the following significant results: 



Ratios of prochlorite from TrnmhnlJ, Connecticut. 



Si02 _ 

 AI2OS 

 FeO _ 

 MgO_. 

 CaO_ 

 MnO_ 

 H,0 _ 



.3929 .3929 1.88 2X .94 



.2080 .2080 1.00 1X1.00 



.3691 ] 



.4365 



.0591 



.0060 J 



.4235 .4235 2.04 2X1.02 



.8707 4.18 4X1.04 



The present mineral then approximates the simple formula : 

 4(Fe,Mg)O.Al,03.2Si02.2H20 



or, 



H. (Mg, Fe), Al, Si,0,3. 



A comparison of the univalent oxides yields further suggestive 

 relationships, for instance : 



Ratios of univalent oxides of prochlorite from Trumbull. 



FeO .3691] 



CaO .05911.4342 1X1.00 



MnO .0060 J 



MgO .4365 .4365 1X1.01 



Thus the prochlorite from Trumbull approximates the composi- 

 tion expressed by the formula : 



2FeO. 2MgO. Al^Oj. 2Si02. 2IL,0 



with the ferrous oxide in small measure replaced by lime and man- 

 ganous oxide. The calculated values to satisfy the above formula are 

 given with the analytical figures opposite for comparison in the 

 next table : 



SiOj 



AI3O3 



FeO (+CaO+MnO). 



MgO 



H2O 



23.69 

 21.26 

 30.27 

 17.60 

 7.6.3 



100. 45 



24 96 

 21.16 

 29.74 

 16.68 

 7.46 



100. 00 



