12 



LARSEN AND STEIGER: MINERALOGIC NOTES 



Chemical properties. Griffithite gelatinizes with HC1. The 

 material selected for the analyses showed under the microscope 

 almost no impurities; its optical properties varied as indicated 

 in the preceding description. The analysis by George Steiger 

 is given in column 1 of table 3; the molecular ratios are given in 

 column 2. 



TABLE 3. 

 Analysis and Molecular Ratios of Griffithite 



The ratios lead to the formula 4(Mg,Fe,Ca)0.(Al,Fe) 2 3 . 

 5Si0 2 .7H 2 for griffithite. Prof. F. W. Clarke has kindly pro- 

 posed the formula H 4 R" 4 R'"* Si 5 0i 9 + 5H 2 0, or 



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R 



R"'; 



,Si0 4 = R" H 

 -Si0 4 = R" H 

 >Si0 3 + 5H 2 



-Si0 4 = R" H 

 Si0 4 = R" H 



