76 NEW YORK STATE MUSEUM 



tooled the color is pinkish white, and letters and designs stand out 

 prominently from the polished surface. The stone is especially- 

 valuable for monuments. 



Mineral and chemical composition. The Picton Island granite 

 is essentially a mixture of feldspar, quartz and biotite, with no 

 marked differences as regards composition between the red and 

 pink varieties. The textures are even and thoroughly massive. 

 The red or medium-grained variety is composed of particles aver- 

 aging 5 mm in diameter and the fine-grained of particles averaging 

 fro'm I to 2 mm. The coloration is due to the feldspar ingredlients 

 which contain minute inclusions of hematite, magnetite, hornblende, 

 garnet, muscovite, titanite, apatite and pyrite are present in S'mall 

 amounts. The pyrite is mostly limited to the joint surfaces and is 

 so sparingly distributed as to exert no appreciable effect upon the 

 durability and permanency of color of the granite. 



The following chemical analysis by W. S. Hall of the Massa- 

 chusetts Institute of Technology is abstracted from a circular 

 issued by the Picton Island Red Granite Company : 



SiOa 69.20 



AI2O3 13.80 



Fe^Os 5-28 



CaO 1. 51 



MgO .Tj 



K2O, Na^O 8.80 



S 04 



H2O and loss .60 



The composition is normal for granite, with the exception of 

 the iron which is a little higher perhaps than is usual in most 

 granites. This is explained by the rather abundant magnetite, in 

 which form the iron can exert no detrimental effect. Although 

 the potash and soda are not separated in the analysis, the former 

 probably predominates as the feldspar is mostly microcline and 

 orthoclase with subordinate plagioclase. Treatment with acetic 

 acid failed to give any reaction for carbonates. 



Physical tests. According to information furnished by the com- 

 pany, the granite has a specific gravity of 2.653. ^ cubic foot 

 accordingly weighs 165.81 pounds, which is about the average for 

 eastern granites. The crushing strength, as determined in a cube 

 taken from the quarries when first opened, is 16,500 pounds a square 



