GEOLOGY OF THE LUZERNE QUADRANGLE 35 



shows: microperthite, 37; oligoclase, 20; hornblende, 25; hyper- 

 sthene, 15 ; magnetite, i ; apatite, i ; biotite, ^ ; garnet, ^t. ', and very 

 little zircon. 



Pegmatite, Aplite and Silexite 



In the preceding descriptions of the rocks, local occurrences of 

 pegmatite, aplite and silexite have been incidentally referred to, and 

 certain of the pegmatite dikes are specifically referred to in the 

 chapter on Mines and Quarries. Pegmatite, and to a less extent 

 silexite, have been observed as dikes and lenslike masses within 

 practically all the rock formations already described. Some ex- 

 amples will now be given. Only the larger observed dikes are rep- 

 resented on the geologic map. 



Grenville limestone is cut by small dikes of granite, pegmatite 

 and silexite near the " Cave " at the southern end of Athol village. 



Pegmatite very commonly, and silexite dikes less commonly, cut 

 the gabbro and metagabbro masses, especially around their borders. 

 Various good examples are mentioned in the preceding discussion 

 of the gabbro and metagabbro. Some of these cut nonfoliated 

 gabbro; some cut across the foliation of the metagabbro; and some 

 are bands or lenses in the metagabbro parallel to its foliation. 



Pegmatite and silexite, especially the former, occur locally in 

 many parts of the areas mapped as medium-grained granite. Most 

 of these are in the form of small dikes or lenses in the granite 

 parallel to its foliation, but occasionally some cut across it. Those 

 parallel to the foliation are, as a rule, not very sharply separated 

 from the granite, while those which cut across usually are. Among 

 many places throughout the granite areas where such pegmatite and 

 silexite masses are clearly shown, a number are mentioned in the 

 above description of the medium-grained granite. 



Some pegmatite and less silexite occur locally in the coarse- 

 grained granite in much the same manner as in the medium-grained 

 granite, but in notably smaller amounts. A locality of special inter- 

 est is nearly a mile southeast of Linwood school where highly foli- 

 ated coarse-grained granite is rather sharply cut across its foliation 

 by a number of long nearly parallel dikes of pegmatite ranging 

 from a few inches to. several feet in width. 



Pegmatite and silexite masses were seldom observed within the 

 areas mapped as syenite and grano-syenite. An exceptional place 

 is the northwestern portion of the large area west of Stony Creek 

 village where many very narrow highly quartzose to silexitic bands 

 lie in the grano-syenite parallel to its foliation and without very 

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