330 Penfield and Sperry — Mineralogical Notes. 



I. II. Mean. Ratio. 



Si0 2 44-82 44'81 44-81 "747 



A1 2 3 10-84 1090 108V -106 



FeO _.__ -35 -28 -31 -004 



MgO 28-91 2889 28-90 '722 



K 2 0. 8-33 8-47 8-40 -089 



Na 2 0__ -33 -46 -38 -006 



Li 2 . _ -09 '01 -08 -003 



H 2 .__ 5-44 5-41 5-42 -301 



Loss at 100° -98 '94 -96 -053 



100-13 



The analysis shows that the mineral is essentially a phlogo- 

 pite but no relation between the constituents can be detected 

 which can be expressed by a simple formula. Comparing it 

 with other analyses, especially the recent ones given in Tscher- 

 mak's article "Die Glimmergruppe "* we notice that it has 

 about the same percentage of Si0 2 , MgO and K 2 0, less A1 2 3 

 and Fe 2 O s , the latter we expect from its unusually light color, 

 more H 2 and no fluorine, which is a little surprising as all 

 previous analyses have shown from 0*8 to over 4*0 per cent 

 of F. 



If we seek out in our analysis the molecules which Tscher- 

 mak regards as characteristic for the micas, 



K = Si 6 Al 6 K 6 24 ratio of Si0 2 : A1 2 2 

 and M = Si 6 Mg 12 24 ratio of Si0 2 : MgO 



we find that they are present in the following proportion 

 together with a residue. 



K 2 



1: 1 



2 • 





K. 



Ratio. 





M. 



Ratio. 



Residue. 



Ratio 



Si0 2 _ 



12-72 



•212 (2) 



Si0 2 



21-77 



•363 (1) 



Si0 2 _l_. 10-32 



•172 



A1 2 3 



10-87 



•106 (1) 



FeO 



•31 



»> 



H 2 5-28 



•293 



K 2 0. 



8-40 



•089^1 



MgO 



28-90 



loss at 100° -96 



•053 



Na 2 



•38 



•006 1 () 

 •003 f * } 

















Li 2 0_ 



•08 





50-98 





16-56 





H 2 0_ 



•14 



•008J 













0) 



(2) 



32-59 



We find that there is 32*59 per cent of the K molecule in 

 which the protoxide is almost wholly K,0, a little Na 2 0, Li 2 

 and H 2 being required to make the ratio 2:1:1. The M 

 molecule is a very pure magnesia silicate while the 16*56 per 

 cent of residue is a very pure ortho silicic acid H 4 Si0 4 , or if 

 desired Si 6 H 24 24 with the ratio of Si0 2 : H 2 = 472 : ;346 = 

 1 : 2-01. It is necessary here to include the H 2 which was 

 lost at 100° C, the analysis being made on air-dry powder. 

 The phlogopites contain more acid than the ordinary micas 

 which are made up of mixtures of the K and M molecules. 



* Zeitschr. Kryst., iii, 143. 



