110 HOW CKOl'S FKED. 



The following analyses represent these varieties. 



Muscovite. Phlogopite. Biotite. 



Litchfield, Mt.Leiiistor, Edwards, N. Burgess, Putnam Co., 



Conn. Ireland. N. Y. Canada. N. Y. Siberia. 



Smith & Brush. IlaiiirP.ton. W.J.Craw. T.S.TIunt. Smith & Brush. H. Rosii. 



Variable Composition of Minerals. — We notice in the 

 micas that two analyses of the same species differ very 

 considerably in the proportion, and to some extent in the 

 kind, of their ingredients. Of the two muscovites the 

 first contains 6°|„ more of alumina than the second, while 

 the second contains 5° |„ more of oxide of iron than the 

 first. Again, the second contains 12. 4" |^ of potash, but no 

 soda and no lime, while the first reveals on analysis 4°|^ of 

 soda and 0.5° 1,^ of lime, and contains correspondingly less 

 potash. Similar differences are remarked in the other anal- 

 yses, especially in those of Biotite. 



In fact, of the analyst's of more than 50 micas which are 

 given in mineralogical treatises, scarcely any two per- 

 fectly agree. The same is true of many other minerals, 

 especially of the ainphiboles and pyi'oxenes presently to be 

 noticed. In accordance with this variation in composition 

 we notice extraordinary diversities in the color and ap- 

 pearance of different specimens of the same mineral. 



This fact may appear to stand in contradiction to the 

 statement above made that these minerals are definite 

 combinations. In the infancy of mineralogy great per- 

 plexity arose from the numerous varieties of minerals that 

 were found — varieties th.it agreed togeilier in certain char- 

 acteristics, but widely differed in others. 



