Eggleston — Eruptive Rocks at Cutting sville, Vt. 389 



in the darker colors. Poikilitic inclusions of pyroxene 

 and, in less amount, biotite and olivine give rise to the 

 luster-mottling visible in the hand specimen. 



Pyroxene is represented by augite of two colors, pale 

 green and pale brown. The colors appear separately or 

 sometimes together in the same grain. A pale brown 

 center may be bordered by pale green, with a zone of 

 inclusions of magnetite and hornblende between the two 

 colors. The differently colored parts are optically con- 

 tinuous and extinguish together. When occurring sep- 

 arately, a maximum extinction angle of 44° for the green 

 and 37° for the brown was observed. The augite and 

 hornblende are remarkably intergrown, the latter sur- 

 rounding augite which in turn incloses grains of 

 hornblende. 



Biotite is in thick tables, besides forming striking 

 intergrowths with hornblende. Its pleochroism ranges 

 from pale yellow to chestnut and deep brown or nearly 

 black. 



Olivine in occasional large grains, partly serpentinized, 

 enters the list of accessory minerals, which also 

 includes magnetite, titanite, apatite, pyrite, and probably 

 pyrrhotite. 



One of the sections includes an irregular area of what 

 is possibly cancrinite derived from original nephelite. 

 This is the only suggestion of the presence of nephelite, 

 indicating that it is seldom, if at all, a constituent. 



Texture and mineralogical composition place the rock 

 among the alkali-gabbros under the head of essexite. 

 Chemical analysis supports this conclusion. 



I II III IV v VI VII 



SiO., 



46-47 



46-99 



48-85 



4400 



49-96 



47-90 



48-64 



TiO., 



2-86 



2-92 



2-47 



1-90 



2-40 



1-91 



1-86 



ALO", 



16-86 



17-94 



19-38 



27-73 



18-83 



16-55 



17-96 



FeA 



3-21 



2-56 



4-29 



2-36 



2-52 



5-67 



4-31 



FeO 



7-72 



7-56 



4-94 



3-90 



6-64 



7-50 



5-58 



MnO 



0-23 



Trace 



019 



008 



0-20 



0-60 



0-19 



MgO 



5-16 



3-22 



2-00 



2-30 



3-52 



4-44 



400 



CaO 



9-45 



7-85 



7-98 



13-94 



7-42 



9-35 



8-89 



Na,0 



4-20 



6-35 



5-44 



2-36 



5-26 



3-23 



4-30 



K„6 



1-35 



2-62 



1-91 



0-45 



2-58 



2-08 



2-28 



H,0+ 



0-45 



0-65 



0-68 



0-80 



0-07 



0-20 



1-34 



H„0— 



0-04 









0-53 







Po"0 5 



115 



0-94 



1-23 



0-20 



0-25 



0-32 



0-65 



CO, 



Trace 















ZrO., 



None 















so 3 



None 





not det. 











ci 



006 















