ANALYSES OF TALC AND MICA. (gg? 



Mr. Vauquelin has published in the Journal des Mines, Analysis by 

 No. 88, an analysis of a flexible lamellar talc, of a silvery ^*"^"^^'"* 

 white when in thin scales, in which he found 



Siiex «.... 62 



Magnesia ♦ 27 



Oxide of iron 3*5 



Alumine ]>5 



Wat**"* - — ^ 



100. 



In regard to the principal parts, the silex and magnesia, 

 these analyses pretty nearly agree : but they differ in Mr. 

 Klaproth finding a much less loss by calcination, and no 

 trace of alumine; while on the other hand Mr. Vauquelin 

 says nothing of potash. 



2. Common mica of Zinnwalde, 



If mica were not formerly distinguished from talc in a 



proper manner, it was partly owing to the opinion given by 



the celebrated Dr. Black, in his Elements of Chemistry, 



that the earth of talc, or magnesia, was always one of the Magnesia not 



component parts of flexible stones. The old analyses of ^^^^"V^^^** 



^ , . . ^ flexible stonee, 



mica tended to perpetuate this errour, as it was always said, 



that mica contained magnesia, and belonged to the raag- 

 nesian genus; and Kirwan, in his Mineralogy, speaks of 

 having found 20 parts of magnesia in 100 of colourless 

 mica. 



Mr. Chenevix even goes so far as to say, that talc and Chenevlx. 

 mica scarcely diff'er, s^nd that he has found in them the 

 same component parts in similar proportions: see Ann. de 

 Chim. XXVIII, 200. And Mr. Haiiy expresses himself Haiy. 

 as follows on the uncertainty between the limits of these 

 two kinds of stone. " The name of talc, like that of spar, 

 has been given to a number of minerals very different in 

 their nature. It has been applied generally to a mineral 

 capable of being divided into thin laminse parallel to one 

 of its faces, as is the case with mica, Venetian talc, sul- 

 phate of lime, Sec. With respect to the species in question, 

 Q 2 the 



