«>0g JIWALYSES OF *ALC ASD MtCA* 



the name of talc was employed in contradistincftioti to ttial 

 of mica; talc signifying a mica in large laminae, and mica 

 a talc in small scales* It was supposed to have been ob* 

 served too, that talc was softer to the feel, and mioa more 

 harsh ; but the point of separation, where talc ceases to be 

 xnica, and mica talc, still remained ttt be determined*'* 



To fix the boundary between these two minerals with 

 accuracy* a strict investigation of the component parts of 

 Comrtioti mica mica was stm requisite. Accoramgi) Mr. Klaproth took 

 fram Bohemia. ^^^^ common mica of Zinnwalde, in the mountains of Bo* 

 liemia, for this purpose* It is found over a tin mine; is of 

 a silvery white mingled with gray | and is crystallized in 

 hexagonical lamince, a little elongated, of an elastic flexi* 

 Jbility, and usually arranged in the form of a rose. 



While this elastic kind of flexibility may serve as one of 

 the external characters to distinguish mica from talc, which 

 has only an ordinary flexibility, the manner in which mica 

 comports itself on exposure to heat is slill more character- 

 Action of heat, istic. When mica is heated redhot, its silvery white is 

 changed to a deeper gray, but no diminution of weight is 

 observed* Before the blowpipe on a piece of charcoal it 

 melts readily into a shining, rounded bead, of a grayish 

 black* Exposed to the heat of a porcelain fnrnace in a 

 clay ctudible, it fuses into a dark opake glass ; and in a 

 charcoal drucible into a semitransparent glass, covered with 

 grains of iron. 



The results of its analysis were 



Component Si'ex ...**.. 47 



part-!. Alumine.............. 20 



Oxide of iron 15*5 



' " ' ■» ' - -... manganese • • • • 1 '75 

 Potash • ^ 14-5 



98-75. 



3. Siberian mica in large lamince. 



^iu<;roTygia;s, The mica in large laminae, or Muscovy glass, called in 

 Russia slinda, differs so much from common mica in the 

 largeness of its laminw, and in its splitting perfectly 



straight, 



