The Rev. S. Haughton's Notes on Mineralogy. 259 



SiUca 1433 4-00 



Peroxides .... 374 1-04 



Protoxides .... 386 1-08 



From whicli it is plain that this felspar is orthoclase. 

 The analysis of the black mica is as follows : — 



Black Mica of Canton Granite. 

 Per cent. 

 Silica ... . . . 35-50 



y 



>0-699 



Alumina .... 

 Peroxide of iron . . 



Lime 



Magnesia .... 

 Protoxide of iron . . 

 Protoxide of manganese 



Potash 



Soda 



Loss by ignition . 



99-81 

 Prom the preceding we obtain^ in atoms, — 



Atoms. Oxygen ratio. 



Silica 789 789 



Peroxides .... 646 646'\„yQ 



Protoxides. ... 699 233 J °'^ 



from which may be deduced the following :— 



|26(3IlO) + 74R2 03} +90SiO^ 



0-789 

 646 



4'^(3RO)+|R2 03lsi03"' 



These formulsc represent the analysis, and are sufficiently 

 near to the formu'?e for the Lepidomelane of Soltmann, and of the 

 black uniaxal micas of Donegal and Leinster, to render it pro- 

 bable that they all are varieties of the same mineral. To show 

 their analogy and difference, the following comparison may be 

 useful : — 



* Quart. Journ. Geol. Soc. Loudon, vol. xv. p. 129. 



