284 UNIVERSITY OF VIRGINIA PUBLICATIONS 



The mineral has been reported from Essex and Orange counties, New 

 York,* as a constituent of quartz veins associated with pyroxene, scapolite, 

 and titanite in the veins of Orange Coimty; in small brown crystals with 

 tourmaline in "granitic veins" w^hich traverse gneiss on North River in St. 

 Jerome, Terrebonne County, Canada;! of frequent occurrence in fine crys- 

 tals in the apatite veins of Templeton and adjoining townships in Ottawa 

 County, Quebec ;t and in small crj^stals in a graphitic vein in the toi^Tiship of 

 North Burgess, Lanark County. f Zircon is also an accessory mineral in 

 many iron ore deposits, especially magnetite, and Hintze| quotes its 

 reported occurrence in several meteorites. 



In many of its occurrences, especially in some pegmatite masses, veins, 

 and contact metamorphism, zircon may have been formed as a product 

 of pneumatolitic processes, and Deveille's methods of sjmethsis given on 

 page 281, indicate a possible pneumatolitic origin of the mineral in some 

 cases. 



Of the several occurrences listed above, (1) and (2) constitute the 

 principal primary sources of zircon. The mineral is foimd in varying 

 amounts in most classes of sedimentary and metamorphic rocks but, except 

 in rare instances, its original source was from preexisting igneous masses. 

 Comparing the characteristics of zircons in igneous and secondary (sedi- 

 mentary and metamorphic) rocks, Trueman§ following Derby ^ points out 

 the use of zircon as a criterion for the identification of the origin of foliated 

 rocks. In the anamorphism of igneous or sedimentary rocks many of the 

 small and stable zircon crystals probably remain essentially unmodified. 



Rock Associatio7is. 



Igneous rocks. Zircon is a common accessory constituent of nearly all 

 classes of plutonic and volcanic igneous rocks. Its grains are generally 

 of microscopic size though not uncommonly of macroscopic dimensions. 

 It is an ordinary constituent of granites and syenites, and occurs in some 

 diorites and occasionally in gabbros, among plutonic igneous rocks ; and in 



* Dana, E. S., A System of Mineralogy, 1900, 6th edition, p. 485. 



t Hoifmann, G. Ch., Annotated List of the Minerals Occurring in Canada (re- 

 printed from Trans. Roy. Soc. of Canada, 1889, vol. vii, sec. iii), Geol. and Nat. Hist. 

 Survey of Canada, 1888-89, vol. iv, p. 66T. 



i Hintze, C, Handbuch der Mineralogie, 1907, p. 1664. 



§ Trueman, J. D., The Value of Certain Criteria for the Determination of the 

 Origin of Foliated Crystalline Rocks, Jour. Geol., 1912, vol. xx, pp. 228-258. 



11 Derby, O. A., On the Separation and Study of the Heavy Accessories of Rocks, 

 Proc. Rochester Acad. Sci., 1891, vol. i, pp. 198-206. 



