Pen field — Interpretation of Mineral Analyses. 25 



and yet mud and shale are not supposed to contain the chemi- 

 cal nucleus of muscovite ; but, rather, they contain constituents 

 suitable for the formation of muscovite. 



It is quite common at the Maine localities to find cavities in 

 quartz and other minerals once occupied by tourmaline crys- 

 tals, and often there still remain in these cavities remnants of 

 the fresh, unaltered tourmaline. The tourmaline fragments 

 appear as if etched, and much material has evidently been dis- 

 solved and carried away. Hence replacement pseudomorphs 

 of muscovite after tourmaline might well result from the sub- 

 sequent filling of such cavities by muscovite. Replacement 

 pseudomorphs are well illustrated by specimens from the Maine 

 localities in the Brush Collection. The specimens referred to 

 exhibit cavities containing remnants of fresh unaltered tourma- 

 line, and as secondary minerals we now find cookeite and quartz 

 deposited on the walls of these cavities, with absolutely nothing 

 to indicate that the material for the formation of the cookeite 

 and quartz was derived from tourmaline, for it could equally 

 well have been derived from lepidolite and other minerals ; in 

 fact the tourmaline originally in a cavity could scarcely have 

 furnished sufficient lithia for the formation of the cookeite, 

 provided that not a trace of the lithia was carried away. The 

 fact, therefore, that pseudomorphs of muscovite after tourma- 

 line have been described, cannot be taken and accepted as 

 proof that tourmaline is closely related to the micas, and that 

 the formula of tourmaline must show close analogies to the 

 formulas of the minerals of the mica group. 



Clarke's formula for the tourmaline acid is H 29 B 3 Si 6 31 , 

 which requires the ratio of Si0 2 : B 2 3 : Total Hydrogen to be 

 6:1-5:29, or 4:1:19-33. It is true that three of the 

 analyses of Riggs yield this ratio (JSTos. 18 and 19, page 22, and 

 also No. 20, if it is assumed, as is by no means proved,* that 

 the titanium exists as Ti 2 3 ). Assuming Ti 2 3 as existing in 

 No. 20, the ratio becomes 4-00 : 0-97 : 19 ; 2. 



These three analyses then, out of a total of twenty by Riggs, 

 alone support Clarke's formula. Two of the three varieties 

 (No. 19, black tourmaline from Pierrepont, N. Y., and No. 20, 

 brown tourmaline from Gouverneur, N. Y.) have been analyzed 

 by Rammelsberg, a fact ignored by Clarke. It may be claimed 

 by some that Rammelsberg's analyses are not to be taken into 

 consideration because they are old. It should be said, how- 

 ever, that Rammelsberg undoubtedly determined the bases and 

 loss on ignition in his analyses with considerable accuracy, and 

 his results need not be wholly ignored. Assuming that SiO„ 

 and B 2 3 are present in tourmaline in the ratio 4:1, it becomes 



*See suggestions by Foote and the author, p. 11T of their article, loc. cit. 



