Spedroscojiic Examination of Silicates, 329 



iu the spectroscope ; for certain minerals seem to resist de- 

 composition in this manner witli great obstinacy ; and, 

 moreover, of the elements, lithium appears to rival sodium 

 in the volatility of its chloride and the persistency of its 

 spectrum band. For instance the variety of muscovite, 

 termed margarodite, from Trumbull, Conn., afibrds a spec- 

 trum with a faint potassium and a strong lithium I)and. 

 This cannot be ascribed to the presence of those alkalies in 

 the relative quantities indicated by their spectra, because 

 the analyses of margarodite (Dana's Min., p. 310) exhibit 

 in some instances as much as 12 per cent, of potassa. In 

 fact the muscovites, as a class, do not yield up their alkalies 

 under the decomposing action of calcic chloride as readily as 

 many other minerals do. For example, we may take the 

 well known specimens from Pennsbury, Chester Co., Pa. 

 When mixed with an equal amount of the paste, this mineraj 

 in powder gave the potassium band faintly, after exposure to 

 the flame for over a minute ; with four times the amount of 

 calcic chloride, it gave the spectrum more strongly than at 

 first; but when mixed with eight times as much, the spec- 

 trum was no stronger than at the beginning. In the case of 

 a muscovite (from an uncertain locality) no potassium band 

 whatever made its appearance. A still more striking illus- 

 tration of what is said above, is afforded by the pink scapo- 

 lites of Bolton, Mass. A compact, beautifully pink, and 

 apparently quite unaltered specimen of this mineral, gave a 

 lithium band, but no potassium. 



We are fortunate in possessing two analyses of this pink 

 scapolite (Dana's Min., pp. 320 and 806). According to 

 one, it contains 4'52 per cent, of soda and 0-54 per cent, of 

 potassa; to a second, 6-55 per cent, of soda, with a little 

 jjotassa. That no doubt might remain, I have analyzed a 

 greenish-white compact translucent wernerite with a spec, 

 grav. of 2.71, from Attlcboro', Bucks Co., Pa., and find 

 that it contains Si Og 47-47; Alg O3 27-51; Fes O3 

 trace; Mg O 1-20; Ca O 17-59; Naa O 3-05; Kg O 1-40; 



