360 BULLETIN OF THE NEW YORK STATE MUSEUM 



NOTES ON THE MICROSCOPIC STRUCTURE 



Granite, Forsythe's Quarry, Grindstone Island, Jefferson 

 County. — Mineral composition : quartz, feldspar (orthoclase 

 and plagioclase) and muscovite ; magnetite accessory. Both 

 feldspars have lost many of their special characters. The 

 cloudiness is not confined to the lines of cleavage but per- 

 meates the whole substance of the mineral. And there are 

 no glassy crystals. The quartz Is full of cavities. It car- 

 ries myriads of acicular crystals, probably rutile. The 

 quartz occurs In a structure known as mosaic — see Saxon 

 granullte for an example. 



Granite, Ausable Granite Works, Keeseville, Essex County.— 

 Norlte (?) constituent minerals : plagioclase, orthoclase, hy- 

 persthene and biotlte ; accessory minerals : hematite and 

 pyrite. The feldspars are almost perfectly fresh, only 

 traces of kaollnlzatlon appearing. The hypersthene Is the 

 next most abundant mineral. This Is very fresh generally, 

 though it shows slight traces of change along the cleavage 

 lines. It has scales of hematite (?) Included. It occurs In 

 bladed crystals, one-eighth to one-quarter of an Inch long ; 

 also In Irregular grains. The biotlte occurs In small, irreg- 

 ular crystals in limited quantity, but fresh looking. The 

 pyrite Is scarce and In small grains only. 



Granite (weathered), Ausable Granite Works, Keeseville, 

 Essex County. — The feldspars are kaollnlzed In spots. 

 Some are mottled throughout, but generally the feldspars 

 are fresh. 



Granite, Hallowell, Maine.— Orthoclase, plagioclase, musco- 

 vite, biotlte and quartz. The feldspars are kaollnlzed much 

 more than they show, microscopically. None of them are 

 fresh throughout. The quartz Is In rough and Irregular 

 grains. Sometimes It Is globular, and Imbedded In the feld- 

 spar. Both the quartz and the feldspar are crowded full of 



