382 PR T. THOMSON on Asbestus, Chlorite, and Talc. 



rated talc ; but the talc contains a quantity of silicate of iron 

 and of silicate of alumina, not to be found in the nephrite. 



We may consider what has hitherto been called indurated 

 talc as an impure variety of nephrite. 



6. Cornish Talc. 



This is a mineral which I got many years ago from Cornwall, 

 under the name of Talc. . The locality was not given ; but I sus- 

 pect it to have been found in the lode of one of the mines near 

 St Austle. 



It has a white colour, with a slight shade of yellow, and con- 

 tains interspersed through it grains of dark purple fluor-spar, 

 and of another mineral which seems to be apatite. 



It is composed of small foliated masses, laid upon each other 

 irregularly. Each of these grains (not above the size of a mus- 

 tard seed) has an imperfect resemblance to a crystal. I fancy I 

 can distinguish in some of them the rudiments of octahedrons, 

 but this may be imagination. 



Lustre rather pearly. 



Translucent ; sectile. 



About the hardness of fluor-spar. 



Specific gravity 2.648. 



Its constituents, from two careful analyses, are as follows : 



Silica, , J0 .^ 4 ?*? 3 J ?* ) . 45.155 

 Alumina, . .-*a r jfo '.*j fi 40.110 

 Lime, . ' ^',i'^ i. .;..;;: 4.170 

 Magnesia, . ^ - , ... .y*- 1.900 

 Protoxide of iron, . . 2.430 

 Water, . . . . . '. 4.250 



98.015 



