42 



NEW YORK STATE MUSEUM 



Thus, according to the old quahtative classification, the rock is a 

 biotite-diabase, while under the new quantitative chemical classifica- 

 tion it is a biotite-camptonose. The amounts of SiOj, AUOg, and 

 CaO in the analysis strongly bear out the determination of the 

 plagioclase as ranging from andesine to labradorite. Such a high 

 content of FeO in the analysis makes it certain that the biotite is 

 rich in ferrous iron, since there is not enough magnetite and augite 

 to account for so much FeO. The sulphur appears too low as judged 

 by the amount of pyrite visible even to the naked eye. The high 

 TiOs shows either ilmenite or that the magnetite is decidedly titan- 

 iferous, though a little of the TiOo may be in the biotite. The low 

 FcoOg content in the analysis favors the presence of ilmenite. 



It is important to note that the analyses of the diabase and typical 

 gabbro are very similar except for somewhat higher silica and lower 

 lime in the diabase, this difference probably being due to the slightly 

 more acid character of the plagioclase in the diabase. Thus the 

 two rocks have quite certainly been derived from the same source 

 of basic supply though at different times. 



Table 12 

 Adirondack diabase analyses compared 



SiOi 



50.57 

 13 58 

 3.26 

 10.09 

 4.98 

 7.67 

 2.92 

 1.89 

 I 10 



AI2O3 



FCiOa 



FeO 



MgO 



CaO 



NajO 



K2O 



H2O 



TiOi 



2 68 



P2O5 



28 



Gl 



.09 

 .09 



'"'."36 



.09 



10 



F 



Cr203.. 



MnO 



BaO 



SrO 



S 



•03 



CO2 



43 

 19 



5 

 6 



5 

 9 

 4 



41 



42 

 72 

 69 

 98 

 II 

 39 

 47 

 00 



35 



99.78 



2.00 



100.54 



44-51 

 19.99 



7.22 

 8. II 

 8.15 

 5-24 

 2.60 



2-93 



45 

 19 



15 

 2 

 8 

 2 



3 

 2 



46 

 94 



36 



95 

 32 

 12 

 21 

 30 



98.75 



99.66 



46-73 

 16.66 



3-56 



8.45 

 8.12 



8.03 



3-73 

 1 .64 



2-39 

 •03 

 •39 

 .18 

 .26 

 .06 

 trace 

 .04 



100.27 



50.89 

 1539 



5-77 

 7.60 

 8.75 

 5.67 

 2.72 

 2.46 



99 25 



