22 NEW YORK STATE MUSEUM 



Quartz syenite. Syenite is conspicuously developed as a mem- 

 ber of the great syenite-granite series throughout the Adirondacks. 

 Typically it is a medium-gramed, more or less gneissoid quartz 

 syenite which is greenish gray where fresh and light brown where 

 weathered. It almost always contains hornblende or monoclinic 

 pyroxene, or both. Since much of the feldspar is usually micro- 

 perthite, the syenite has a strong monzonitic affinity. The quartz 

 content varies considerably from a few per cent to 20 or 25 per 

 cent when the rock becomes a grano-syenite. A distinct porphyritic 

 texture may be locally developed. Foliation may be practically 

 absent, or it may be moderately to highly developed. The color 

 may locally be light gray to pinkish gray. Granulation is common 

 though extremely variable. Granulation is usually most conspicu- 

 ously developed in the feldspars and less so in the quartzes. 



Typical quartz syenite, with usual variations as above described, 

 is well developed in many areas throughout the Luzerne quadrangle 

 (see map). It is, however, subordinate to the granite. In the fol- 

 lowing descriptions, where certain small areas and portions of 

 larger areas are not mentioned, it may be taken for granted that the 

 observed outcrops of syenite are mostly the rather normal rock. It 

 can not be too strongly emphasized that boundary lines between the 

 syenite areas and areas of granite and mixed rocks are rather arbi- 

 trarily drawn on the geologic map because almost never are there 

 anything like sharp contacts between these rock types. 



Just west of Mount Anthony a small area contains ver)?- gneissoid, 

 biotitic grano-syenite cross-cut by some pegmatite dikes without 

 sharp boundaries. 



Most of the syenite of the area near Hartman is rather normal 

 except toward the north where it locally varies almost to granite 

 carrying some garnets and some fragments of amphibolite. 



The main body of rock in the small area just south of Hadley 

 village is medium-grained, well-foliated, greenish gray quartz sye- 

 nite or grano-syenite containing some bands rich enough in quartz to 

 be classed as granite. No. 7 of the accompanying table shows the 

 minerals contained in a thin section of this syenite. 



The rock of Cobble mountain just east of Lake Luzerne is 

 medium grained, brown, moderately foliated, and very homogene- 

 ous in great ledges. A thin section (no. 13 of the table) shows it 

 to be unusually rich in hornblende and plagioclase so that it is really 

 a quartz-hornblende monzonite which is quite certainly a facies of 

 the normal syenite. 



