5o8 



NEW YORK STATE MUSEUM 



showed it to have similar mineralogy, quartz, feldspar, p)Toxene, 

 mica, zircon, titanite, graphite and apatite being present. The 

 pyroxene is white instead of green and probably differs consider- 

 ably from that previously discussed and analyzed. The mica is 

 unquestionable phlogopite. Some of the feldspar, about 20%, was 

 badly altered, showed no sign of twinning, and was assumed to be 

 orthoclase. The remainder was twinned plagioclase with 12 maxi- 

 mum extinction angle, and is regarded as andesin, Ab 2 An z , though 

 it is possible that it may be albite. The analysis is therefore some- 

 Mode of quartz-pyroxene-phlogopite gneiss (i-L-3-a) 



Units 

 Units measured Sp. Gr. by weight % weight 



Quartz 699x2.65 = 1852 = 30.22 



Feldspar 420x2.64 = 1109 = 18.10 



Pyroxene 642x3.3 = 2 119 = 34.56 



Phlogopite 347x2.85 = 989 == 16.13 



Titanite 10x3.5 = 35 = ° ■ 57 



Zircon 4x4.5 = 18= 0.29 



Apatite e 2x3. 2 = 6= 0.10 



Graphite 1x2.4 = 2 = 0.03 



Total 2125 6130 100.00 



Composition calculated from mode 





Qz. 



Pyrox. 



Phlog. 



Orth. 



Alb. 



Anor. 



Tit. 



Zir. &Ap. 



Total 



Si0 2 



A1 2 3 . . 



30.22 



18.75 



1 .07 

 0.65 

 2.25 

 6.48 

 4.80 



o.35 

 0. 10 

 . 11 



7.71 

 1.87 



2-34 

 0.65 



6.67 



1.84 



2 . 12 



1 74 



0. 19 



O.09 



68.09 

 7.17 

 0.65 

 2.30 



11 .45 



Fe 2 3 . . 









FeO 





.05 

 4-97 













MgO 















CaO .... 









0.97 



. 16 



O .06 



5-99 

 i-57 

 2 . 19 

 . 11 



Na 2 0.. . 





0.08 





1. 14 



K 2 0... . 





1. 45 0.64 









Mn0 2 .. . 













Ti0 2 . . . 





1 







O . 22 



O . 20 

 O.03 



. 22 



Zr0 2 . . . 







- 







. 20 



P 2 5 . . . 















0.03 













Total . 



30 . 22 



, 34-56 



16.13 



3-63 



9-^5 



4-8 3 



0-57 



O.38 



99-97 



what uncertain and its result is of itself pretty good evidence that 

 the pyroxene is of quite different character from that analyzed and 

 used in the calculation. The lime-magnesia ratio seems clearly 

 quite erroneous. If the lime and magnesia percentages in the 

 pyroxene calculation are reversed, bringing it more closely into line 

 with the composition of ordinary diopside, this anomaly disappears. 



