£. Weidman — Irvingite, a New Variety of Lithia-mica. 453 



1. Irvingite from Wausau, Wis., anal, by V. Lenher. 



2. Polylithionite from Kangercllaursuk, Greenland (quoted by 

 Dana's Min., 6th ed. p. 627). 



2a. Polylithionite from Narsarsuk, Greenland, anal, by Flink 

 (cited Jour. Chem. Soc. (London), vol. lvii, p. 412, 1900). 



3. Lepidolite from Rumford, Me., anal, by Riggs (quoted by 

 Clarke, U. S. Geol. Survey, Bulletin 220, p. 73). 



4. Cryophyllite from Auburn, Me., anal, by Riggs (quoted by 

 Clarke op. cit., p. 74). 



5. Zinnvvaldite, from Zinnwald, Bohemia (quoted by Dana's 

 Min., 6th ed. p. 626). 



It will be observed upon comparing the analysis of the lithia 

 mica from this locality with the analyses of other varieties of 

 lithia-mica, that each has characteristic chemical features not pos- 

 sessed by the others. The cryophyllite, 4, and zinnwaldite, 5, are 

 characterized by high content of iron and low sodium, while 

 the lithia-mica, 1, and polylithionite, 2, are essentially free from 

 iron and are high in sodium, and lepidolite, 3, is low in sodium 

 and free from iron. The lithia-mica from this region, 1, 

 differs essentially from polylithionite 2 and 2a in containing a 

 higher "content of alumina and lower fluorine, as well as pos- 

 sessing different proportions of the alkalies : it differs from 

 cryophyllite, zinnwaldite and lepidolite in its higher content of 

 silica and soda. 



On the whole, this mica 1 differs essentially from the other 

 varieties of lithia-fluorine micas, apparently being a new vari- 

 ety of this interesting group of minerals, and the name "Irving- 

 ite" after R. D. Irving, is proposed for it. Prof. R. D. Irving's 

 principal geological work was done in Wisconsin, and hence 

 it seems appropriate that this new mineral from Wisconsin be 

 named after him. 



Theoretical Composition of Irvingite. — The percentage com- 

 position and the molecular ratios of the constituents of this 

 lithia-mica have already been stated. Prof. F. W. Clarke has 

 pointed out that the trisilicate molecule dominates in all the 

 lithia-micas. ]STot one of them approaches a full orthosilicate, 

 and in nearly all the Si0 2 ratios fall below the metasilicate 

 proportions. 



The late Prof. S. L. Penfield, who examined this mineral 

 and analysis, pointed out that the analysis yields a ratio of 

 Si0 2 : A1 2 3 : R 2 : (F.OH) approximately as 6 : 1 : 2 : 1. Accord- 

 ing to Pentield, the ratio corresponds to a formula of a trisili- 

 cate, 3Si a O(Al.(FOH)y O.R 2 0. The alkalies in R 2 approx- 

 imate the following ratios : K 2 : Na 2 : Li 2 as 1 : 1 : 2 and in 

 (F.OH) F : OH as 3 : 1. Assuming these proportions, the cal- 

 culated approximation to the theory to the above ratios is 

 shown in the following table : — 



