374 DR T. THOMSON on Asbestus, Chlorite, and Talc. 



III. TALC. 



The terms Talc and Mica seem originally to have been ap- 

 plied indifferently to the same minerals ; namely those which 

 could be split into thin layers or plates. When the plates were 

 large, the mineral was called Talc, when they were small it was 

 called Mica. Common talc, or Venetian talc as it is called, seems 

 first to have been constituted a peculiar species by WERNER. 

 CRONSTEDT has considered it as a variety of mica. HAUY, in the 

 iirst edition of his Traite de Mineralogie, published in 1801, ar- 

 ranged under talc several other minerals that are probably dis- 

 tinct species ; namely, Chlorite, Agalmatolite, Steatite, &c. 



1. Venetian Talc. 



This mineral is found imbedded in serpentine, in the moun- 

 tains of Saltzburg and the Tyrol, and was formerly carried to 

 Venice as an article of commerce, being employed in medicine. 

 Hence the name Venetian Talc. It was chiefly employed as a 

 cosmetic. It was reduced to a fine powder by heating it to red- 

 ness, and afterwards pounding it in a hot mortar. 



Colour apple-green, It is composed of thin flexible plates, 

 having a silvery appearance and a pearly lustre, and easily sepa- 

 rable from each other. These plates are not elastic. It varies 

 from semitransparent to translucent. Very sectile. Soft enough 

 to be scratched by the nail of the finger. Specific gravity 2.697- 

 Infusible before the blowpipe per se. 



I have never seen a specimen of true Venetian talc in crys- 

 tals. 



A very pure specimen of this mineral being subjected to ana- 



