FfP ] 3 1902 



No. 6. — Contributions from the Harvard Mineralogical 

 Museum, VI. 



Leucite-Tinguaite from Beemerville, New Jersey. By John E. Wolff. 1 



Introductory. 



The post-Cambrian eruptive rocks of Sussex County, New Jersey, have 

 been the subject of several interesting papers, 2 which have described the 

 elaeolite-syenite and some of the associated rock masses (ouachitite), and 

 several of the dikes, but not the rocks of the whole complex. In 1896 

 and other years the writer was engaged with the areal geology of this 

 region and made rock collections from the old localities and from several 

 new ones discovered in going over the ground ; a list of which with map 

 has been published. 3 He hopes to complete the description of this 

 material, of which the present paper forms the first instalment. 



Leucite-Tinguaite. 



This rock occurs as a dike in the main mass of the elaeolite-syenite 

 two miles northwest of Beemerville, and near the southwest end of the 

 syenite. It was found in a field just under the 1300-foot contour of 

 the topographic map and a short distance east of the road over the 

 mountain. The dike is fifteen inches wide, cutting coarse syenite, with 

 a strike N. 35 "W. and dipping 45 northeast ; it is exposed for but a 

 few feet. 



The rock has a dull greasy green color, is dense grained and contains 

 distinct phenocrysts of nepheline in hexagonal prisms and large pheno- 

 crysts of pseudo-leucite, which weather white on the rock surface and 

 are greenish white in the fresh rock ; they have a diameter of fifteen 

 centimeters at the maximum and occur in bands parallel to the walls 

 of the dike. Their form is that of the leucite eikositetrahedron, the 

 crystal forms rather perfect, and the outlines linear and sharp in cross 



1 Published by permission of the Director of the U. S. Geological Survey. 



2 B. K. Emerson, Amer. Journ. Sci., 23, p. 302 and 376, 1882. J. F. Kemp, 

 Amer. Journ. Sci., 38, 1889, p. 130; the same, Trans. N. Y. Acad. Sci., 11, p. 60, 

 1892 ; Amer. Journ. Sci. 45, 1893, p. 298 ; Amer. Journ. Sci., 47, 1894, p. 339. 



» Geol. Survey N. J. Annual report, 1896, p. 91. 



VOL. XXXVIII. NO. 6 



