jb. W. Clarke — Minerals of Litchfield, Maine. 271 



tution derivatives of the normal salt Al 4 (Si0 4 ) 3 . The latter 

 contains the fundamental nucleus Al(Si0 4 ) 3 , which appears to 

 be capable of a sort of polymerization, and which forms the 

 basis of the subjoined symbols. 



/Si0 3 -Na /CI /C0 4 =NaH 2 



Al-Si0 4 =Al Al-Si0 4 =Al Al-Si0 4 =Al 



X 3i0 4 =Na 3 /Si0 4 =Na 3 / Si0 4 =Na 3 



Al^Si0 4 =Al Al-Si0 4 =Na 3 Al^Si0 4 =Al 



)Si0 4 =:Na 3 )si0 4 =Na 3 X Si0 4 =NaH 



Al-^Si0 4 =Al Al-Si0 4 =Al <j a 



;Si0 4 =Na 3 )Si0 4 =Na 3 i 



AlfSi0 4 =Al Al^-Si0 4 =Al A!/^ 4 -^ 11 



X SioJ-Na. X C1. Al-Si0 4 =Al 



3 /Si0 4 =Na 3 



Al-Si0 4 =Al 

 X C0 4 =NaH 3 . 



Nephelite. Sodalite. Cancrinite. 



Now although these formulae fit the analyses, and express a 

 structural similarity of type, two of them are capable of a 

 further generalization. Remembering the reciprocal variations 

 between soda and lime in different cancrinites, and the fact 

 that a soda cancrinite is quite possible, we may write the fol- 

 lowing general formula for that species; Al 4 (Si0 4 ) 4 C0 4 lSIa s H 3 ; 

 which requires 



Si0 35-8 



A1 3 3 30-4 



N"a 3 .. 23*1 Partly replaceable by CaO. 



C0 3 ti-6 



H 3 4-1 



Comparing this with Bamberger's sodalite formula, and with the 

 generally accepted formula for nosean, we have this remarkable 

 series of structural expressions. 



/S0 4 -Na /CI. /C0 4 = NaH 3 



Al-Si0 4 =Al Al-Si0 4 =Al Al-Si0 4 =Al 



/Si0 4 =Na 3 )Si0 4 =Na 3 )Si0 4 =Na 3 



Al-Si0 4 =Al Al{-Si0 4 =Al AlfSi0 4 =Al 



x Si0 4 =Na 3 . x Si0 4 =Na 3 . X Si0 4 = Na 3 H. 



Nosean. Sodalite. Cancrinite. 



The formula of hauynite of course reduces to the same type, 

 and so also, probably, does that of microsommite. Hydro- 

 nephelite has a still simpler formula, which, however, includes 

 three molecules of water of crystallization. It may be advan- 

 tageously compared in series with its parent minerals, in which 

 case we have the following set of structures : 



