171 



TAB. CCCXCIV. 



S I L E X Mica. 

 Silvery Mica, 



I n the description of tab. 80, we noticed the difficulty of 

 imitating the lustre of this substance ; but having found 

 means of partly surmounting that difficulty, we are happy 

 to produce examples in the present figure. This one is a 

 curious aggregation of laminated crystals, if I may so call 

 them, it is also very remarkable for being one of the first 

 examples of Mica showing an inclination to mackle. In 

 the present instance the plates are chiefly aggregates "of 

 smaller rhomboidal ones; the mackle forms by the sides 

 of the rhombs being contrary to each other, like some of the 

 Gypsums. See the lower figure of tab. 223, which seems to 

 depend upon similar laws of crystallization. 



This is sometimes found in very large masses. I have 

 specimens six inches long from Aberdeen.— Schorle is oc- 

 casionally included in it. 



I have lenticular crystals of this substance in an ordinary 

 specimen, which, as they certainly are but little if at all 

 noticed, I mention here. They are seemingly formed of 

 the laminae placed a little irregularly edgewise, resembling 

 the lenticular Sulphate of Barytes and some specimens of 

 Talc, which latter is however generally smaller, see tab. 182, 

 where they nearly approach this figure, or rather in tab. 74, 

 under the name Chlorite ; see description, p. 154. I do not 



