PETROGRAPHIC PROVINCE OF NEPONSET VALLEY, MASS. 139 



Comparison of Chemical Composition of Granite and Peripheral Facieb. 



SiO, . . 



A1,0,. 



Fe,0, . 



FeO . . 



MgO.. 



CaO.. 



Na,0. 



K,0.. 



H,0 + 



H,0- 



CO,.., 



TiO,. . 



P,0, . . 



MnO.. 



I. 



100.55 



II. 



76.52 



12.30 



0.70 



0.56 



0.16 



0.31 



5.19 



4.58 

 0.41 



0.11 



0.12 



trace 



100.96 



I. Normal granite — Neponset Valley. 



II. Fine-grained granite or micro-granite — Neponset Valley. 



III. Rhyolitic facies of granite — Neponset Valley. 



ill. 



71.63 

 13.71 

 2.09 

 1.76 

 0.19 

 1.31 

 3.24 

 4.49 

 0.51 

 0.08 



0.41 



0.34 

 trace, less than 0.10 



99.76 



Norms. 



Quartz 



Orthoclase . . 



Albite 



Anorthite. . 

 Wollastonite 

 Enstatite . . . 

 Magnetite. . 

 llmenite. . . 

 Hematite . . . 



I.b. 



24.72 



22.80 



40.87 



5.00 



1.28 



1.60 



2.09 

 0.76 



0.48 



99.60 



Acmite 



Sodium metasilicate 



Diopside 



Hypersthene 



Il.b. 



30.48 

 27.24 

 37.73 

 1.85 

 0.98 

 1.43 

 0.60 

 0.15 



100.46 



I.b. Arfvedsonite-biotite-grano-lassenose. Class 1, order 4, 

 Il.b. Grani-liparose. Class 1, order 4, rang 1, subrang 3. 

 IILb. Phyro-toscanose. Class 1, order 4, rang 2, subrang 3. 



rang 



Ill.b. 



Anorthite . 

 Corundum 



Magnetite 



32.16 

 26.69 

 27.25 



6.39 

 1.12 



1.42 

 0.61 

 1.42 



97.06 



Quartz 



Orthoclase . . 

 Albite 



Anorthite . . . 

 Biotite 



Arfvedsonite 

 Magnetite. . 



100.00 



I. a. 



Il.a. 



IH.a. 



Neponset 



Mode. 



II. a. 



32.31 



27.33 



34.74 



1.64 



3.70 



.28 



100.00 



facies 



micro-granite, Neponset Valley, 

 lite, Neponset Valley. 



Ill.a. 



30.5 



26.5 



27.7 



6.5 



6.8 



2.0 



100.00 



A comparison of the chemical composition of these three granitic facies 

 instructive in its bearing on questions of magmatic differentiation. 



