288 UNIVERSITY OF VIRGINIA PUBLICATIONS 



are traceable directly to the granite. Bayley* remarks that most of these 

 minerals are found in the ore occurring within the limestone. Zircon has 

 been found in many of the magnetite mines of New Jersey,! usually in 

 small crystals and in sparing quantity. 



Zircon is reported by Newland and KempJ along with apatite, titanite, 

 and pyrite as among the less important constituents of the magnetite ore 

 bodies of the Chateaugay mines near the western border of Clinton County, 

 New York. 



Pegmatites. 



The occurrence of zircon in pegmatite masses, especially those of the 

 granite and syenite families, is recorded by many observers. The mineral 

 occurs both as minute inclusions in the principal rock-forming minerals, 

 chiefly quartz and feldspar, and as a megascopic constitutent. As already 

 noted, it has been observed in close association with riebeckite in the peg- 

 matite § masses of the Quincy, Massachusetts, granite. The zircons are 

 very abundant in the quartz-rich portions of the pegmatites, occurring in 

 the feldspar and riebeckite, but chiefly in the quartz as quartz-zircon inter- 

 growths. Some of the zircons were of macroscopic size, the grains measur- 

 ing up to 3 mm. in diameter. Fluorite and ilmenite occur with the zircon 

 and quartz, and the authors state that the "zircon-quartz groups evidently 

 belong to the pneumatolitic period and represent, it is believed, zircon crys- 

 tals which subsequent to their formation suffered more or less recrystalli- 

 zation, replacement by quartz, and perhaps granulation" (p. 131). 



In discussing the genesis of riebeckite and riebeckite rocks Murgoci1[ 

 mentions pegmatitic, micropegmatitic or granophyric structures as charac- 

 teristic, and remarks that riebeckite is a mineral which requires pneumato- 



* Bayley; W. S., A^. J. Geol. Survey, 1910, vol vii, p. 116. 



t Nason, F. L. and Ferrier, W. F., Amer. Asso. Ado. Set., 1890, p. 244; see also 

 Ann. Report of the Stale Geologist, 1868, p. 323; former reports by Rogers; and report bj' 

 Bayley, W. S., 1910, vol. vii. 



t Newland, D. H. and Kemp, J. F., Geology of the Adirondack Magnetic Iron 

 Ores, Bull. 119, N. F. Stale Museum, 1908, p. 114; see also Kemp, J. F., The Geology 

 of the Magnetites near Port Henry, N. Y., etc., Trans. Amer. Inst. Min. Engrs., 1898, 

 vol. 27. 



§ Warren, C. H. and Palache, C., The Pegmatites of the Riebeekite-Aegirite 

 Granite of Quincy, Mass., U. S. A. ; Their Structure, Minerals, and Origin, Proc. Amer. 

 Acad. Arts andSci., 1911, pp. 125-168. 



1[ Murgoci, C. M., On the Genesis of Riebeckite and Riebeckite Rocks, Amer. 

 Jour. Sci., 1905, vol. xx, pp. 133-145. References to the literature are cited by the 

 author. 



