154 



Sec. : see figures. It sometimes has the laminae bent. Its 

 lustre is of the changeable kind ; the upper plates showing 

 the accumulated refracted silvery opacity between those 

 beneath, each plate being transparent if separated*. It is 

 flexible and elastic ; the plates, when bent, will return to 

 their places with a considerable spring (see lottom figure, 

 a plate bent thus much will return — the straight line seen 

 through shows its transparency) : this elasticity, and its 

 being destitute of unctuosity, distinguish it from Talc, as 

 hithe,rto the varieties of one species have been placed among 

 those of the other bv several mineralogists. 



Muscovy Talc of the older authors is undoubtedly Mica, 

 so named in contradiction to Venetian Talc ; which, al- 

 though nearly allied, is yet a distinct species, and may be 

 looked on as a good sample of Talc. 



TAB. CLXXXI. 



1 his specimen differs very little from the Mica from 

 Muscovy, which is occasionally found some feet in diameter. 

 Scotland and Cornwall produce it three or four inches 

 square, or even larger. This kind of Mica is used for lan- 

 terns, &c. and is very convenient for ships, as it bears the 

 explosion of cannon without cracking. It is however liable 

 to get scratched, and becomes rather opaque by heat; which 

 opacity is not removed by water. This substance is spoken 

 of as introduced into Rome in the time of Seneca to admit 



* Its fine lustre we cannot imitate without hazard of the colour 

 changing ; we therefore must request our friends to consider the shining 

 parts of the plate as of a fine silvery or pearly lustre. 



