ANALYSES OF Ti.LC AND MICA. ^^g 



Btraight, that a chemical anal ysis was requisite, to deter- 

 mine whether it be in reality a variety of mica. It is chiefly 

 used in Russia and Siberia inb1:e&d of glass for windows, on 

 which account it is an article of trade, it is found in the 

 remotest parts of Siberia, on the other side of the river 

 Lena, and almost always near the rivers Vitim and Mama, 

 It occurs in a coarse-grained granite, and m large masses of 

 quartz, either in nodules of d'itferent sizes, or in iLidt la«. 

 minai lying in various direct) lons. It is got out with the 

 mallet and chisel. As the ro(-'k is very hard, it is wrought 

 only to the depth of a fathom by Russian colonists, who 

 form companies for this purpiose, and go and reside in the 

 neighbouring woods during the summer. After the mica is 

 got out of the quarry, it is s<orted according to the size and 

 clearness of the plates, and l.hen carried to market, chiefly 

 at Irkutzk, whence it is sent to various places. 



The pieces fresh taken from the quarry, and not split, 

 have a smoky or brownish colour, are ©pake, and reflect 

 objects like a mirror; but in thin plates the colour disap* 

 pears, arjd the mica is transparent. Their price varies con* 

 biderably, according to the size of the plates ; some are 36 

 or 40 inches square ; but in general they are only three or 

 four inches, and such as are less than this are worth very 

 little. 



Before the blowpipe, on charcoal, Muscovy glass loses Action of hea^ 

 its transparency, and becomes of a silvery white, but does 

 not melt like common mica. If large plates of mica be 

 heated redhot in crucibles, or on charcoal, they acquire a 

 striking appearance of thin laminae of silver^ and experience 

 a loss of 1-25 per cent. This mica is infusible even by the 

 heat of a porcelain furnace. In a charcoal crucible, ir^ 

 which several of these lamina, rolled one upon another^ 

 had been placed, the outer ones were found of a gvay co-» 

 lour, glazed, and fragile; the inner ones were as blsvck as 

 tinder, and flexible. In a clay crucible all were hardened, 

 vitrified, fragile, and sonorous; and their colour was of o, 

 grayish white, the surface only b^ing in part light brown. 



The 



