SOS _ Outlines of the Mineralogy and Geology 



of grej or reddish white, which, hy long exposure to the atmos- 

 phere, becomes brownish. 



HI. The Feldspar presents several colours ; generally it is red- 

 disli, sometimes cochineal red ; frequently whitish, and often with 

 a tinge of green ; the latter colour is produced probably in some 

 cases by Epidote, and in others by Hornblende; these several col- 

 ours often occur in the same specimen.- The lustre of the Feld- 



■ 



spar is glistening, approaching to shining, pearly, and sometimes 

 it has a greasy aspect ; its structure is more or less perfectly foil- 

 ated. The Quartz has usually some shade of white, or of black- 

 ish grey; it is also often colourless and transparent, with a per- 

 fectly vitreous lustre. The predominant colour of the Hornblende 

 is greenish black; it is however often bluish grey, and sometimes 

 velvet black and broccoli brown ; its structure is foliated and 



+ 



granular, and its lustre is glistening or dull. 



IV. The proportions of the various ingredients are no less va- 

 rious than their colours ; generally the Feldspar predominates ; 

 next in quantity is the Quartz, and lastly the Hornblende ; in that 

 variety, where there is a reddish Feldspar, the Hornblende is oft- 



tirely excluded, the Quartz present in a small quantity only 



principally of Feldsp 



7 



V. The structure of Sienite varies from very fine 

 granular; in the latter case, the Feldspar, and 



are in 



nearly equal proportions, and sometimes the three constituents 

 are equally al>undant ; in the finer varieties, the Hornblende 

 principally predominates, and the mass appears almost homo- 

 geneous. 



■f 



VI. The above description applies to the Sienite, found prin 

 pally on the north and south of Boston ; it forms the great rai 



ge 



