154 



Outlines of the Mineralogy and Geology 



Geolos^ical Situation and Localities. 



Mica forms a constituent part of Grranite, at Carlisle, where 



it is found in lamina several inches square; it is disseminated 

 also in Limestone at Chelmsford. Small quantities occur in 



» 



Greenstone, at Watertov n and Waltliam ; and in Sienite on the 

 Newburyport turnpike. The black varieties are frequently found 

 io Quartz, at Brighton and Charlestown. The alluvial soils bor- 

 row from Mica tlie beautiful spangled appearance, which they so 

 frequently present. 



SPECIES IV.— SCHORL. 



Common Schorl, CkavelanJ, p. 26t. Jameson^ vol. i. p. 1£1. Schorl, ICiv- 

 ii-an, vol. I. p. 265. Common Schorl, Aikin, p. 233. 



External Characters. 



Its colour is velvet black. 



Its lustre is shining and vitreous. 



It is opaque. 



It occurs crystallized in long, slender, triangular, prisms with 

 vex sides, and in cylinders. The crystals are seldom well de- 



fined 



are 



th difficulty separated from 



bed without 



destructio 



they are long slender and frequently 



each 



fine grained uneven ; the 



other, and their most usual form is a cylind 

 or more sides. 



The cross fracture is 

 fracture is foliated. 



r 



It is brittle. 



It is easily frangible. 





pressed 



& 



al 



