ELIZABETHTOWN AND PORT HENRY QUADRANGLES 4/ 



it is very abundant, and the rock becomes a granite, or of granitic 

 coniposition. In these the quartz is very abundant. Again in the 

 basic extremes, it fails, and in the true syenite phases, the most 

 characteristic of the series, it is rare or absent. 



The most prominent of the dark minerals is a beautiful and 

 striking emerald-green pyroxene. It has the high extinction angles 

 of augite, and sometimes a faint pleochroism to yellow. Experience 

 gained in recasting analyses leads to the conclusion that the jadeite 

 molecule, NaoO, AUOg, 4Si02, is present m its composition, and 

 may be largely responsible for the beautiful green color, so sugges- 

 tive of aegirite. The pyroxene often changes to chlorite and when 

 present in the bodies of magnetite associated with the syenites, it 

 yields red oxid of iron and stains the ore red by filtering into the 

 cracks in the neighboring minerals. It has the same effect on the 

 syenitic rocks, especially those associated with the ore. Under the 

 miscroscope the reddish tinge can be traced back to the chloritized 

 pyroxene. 



Hypersthene is occasional in the syenites, but scarcely so abun- 

 dant as to require extended description. Hornblende, however, is 

 very common. It is a deep brown variety and in the basic types 

 may be more abundant than pyroxene. Biotite is known but is 

 subordinate. The basic phases have it more abundantly than the 

 acidic. It is deep brown in color, but not otherwise remarkable. 



Among the accessories titanite is sometimes extremely abundant. 

 To the unassisted eye it might be taken for garnet, and in the acidic 

 phases, associated with the magnetites, it makes this impression, but 

 the microscope, of course, reveals its identity. Apatite is at times 

 noticeably abundant but presents no peculiarities worthy of special 

 remark. Zircon favors the acidic extremes. Magnetite is in all 

 varieties, even the most acidic, where, unless sharply observed, it 

 might be mistaken for a dark silicate. Pyrrhotite is rarely to be 

 detected. j 



In earlier experience it was believed that garnet was practically 

 limited to the anorthosites and basic gabbros, but as the tendency 

 of the syenites to develop basic phases has been appreciated and 

 the dark hornblendic gneisses have seemed to be, in part at least, 

 referable to them, garnet has been recognized as one of their 

 minerals. While, the reaction rims, which will be more fully 

 described under the basic gabbros, are far more abundant in these 

 latter rocks, yet some cases have been observed in which they were 

 also apparent in the syenitic gneisses. Some dark, hornblendic 

 gneisses have, in the later field work, shown such relationship as to^ 



