QUARRY MATERIALS OF NEW YORK III 



In physical appearance the granite is characterized by a fine grain, 

 medium gray color of body that is well blended, and massive to 

 faintly gneissoid texture. Small crystals of garnet are sparsely 

 scattered through the mass but are noticeable only on close view. 

 There are few streaks or discolorations apparent in the exposure. 



Microscopic examination. The rock consists essentially of 

 feldspar, quartz and biotite in order of importance, with garnet as 

 an accessory which has probably been formed by a partial recrystal- 

 lization of the minerals caused by compression exerted upon the 

 boss after its intrusion. The feldspar and quartz are in irregular 

 particles closely interwoven. Their average diameter is about 5 mm. 

 The biotite is in very fine beds, sprinkled like dust through the gray 

 groundmass. The texture is close and firm. 



The feldspar minerals include microcline, microperthite and ortho- 

 clase as representatives of the alkali class and an acid plagioclase 

 which has subordinate importance to the others. They are but little 

 altered. The biotite is somewhat bleached or partly changed to 

 chlorite. The absence of pyrite or other igneous ingredients is 

 noted. 



Physical tests. The granite from this quarry has a specific 

 gravity of 2.68, ratio of absorption .3 per cent, and pore space 

 .792 per cent. 



ROUND ISLAND GRANITE 



Round island, in the Hudson just above Peekskill, is made up 

 of granite which at one time was actively quarried for crushed 

 stone. The quarry was worked up to ten years ago by Daniel 

 Donovan of Kingston. The site of the quarry was not visited by 

 the writer and there are no details available as to the character 

 of the stone aside from the following chemical analysis, supplied 

 by Mr Donovan : 



Si0 2 63.19 



Al 2 Os 10. 50 



Fe 2 3 10 . 97 



FeO 1. 51 



CaO 6.12 



MgO 1.44 



K 2 4.02 



Na 2 1.02 



Loss .18 



Undet .15 



100. (X) 



