MAGMATIC DIFFERENTIATION IN HAWAII 



301 



Lherzolitic nodules in the summit lavas of Mauna Kea. — The 

 chief difference between the andesitic basalt and the trachydoler- 

 ite is mineralogical ; orthoclase is an essential constituent in the 

 latter, and has wholly, or almost wholly, failed to individualize 

 in the basalt. The two types are almost alike chemically. They 

 also resemble each other in carrying rather numerous ultra-femic 

 nodules of all sizes up to 10 cm. in diameter. These are always 

 rounded and usually roughly spherical, of coarse grain, and of a 



TABLE IV 



Si0 2 .... 

 Ti0 2 . . . 

 A1 2 3 . . . 



FeA--. 

 FeO .... 

 MnO.. 

 MgO 

 CaO ... 

 Na 2 0..., 



K 2 



H 2 0- ... 

 H 2 0+... 



PA 



C0 2 



NiO 



Cr 2 3 .... 

 CuO, etc 



Sp. gr. 



50.92 

 2-55 



59 



•35 

 79 



.40 

 None 

 None 

 None 



100.30 

 2. 761 



032 



173 

 024 



o93 

 001 



097 

 125 

 069 



003 



99.99 



Calculated Norm of i 



Orthoclase 11. 12 



Albite 36.16 



Anorthite 23 . 35 



Diopside 6 . 98 



Hypersthene 7.21 



Olivine 2 . 98 



Ilmenite 4.86 



Magnetite 5-57 



Apatite 93 



Water 1 . 14 



100.30 



1 Trachydolerite, lava flow at 13,000-foot contour on Mauna Kea. 

 i<z Molecular proportions in 1. 



2 Average of 34 analyses of trachydolerites named as such in the third edition of Rosenbusch's Ele- 

 mente der Gesteinslehre. 



3 "Andesite" from Waimea, Kohala district, in northwestern Hawaii. 



dark green or brownish-green color. They seem to be rather 

 uniformly composed of dominant olivine, much diallage, subor- 

 dinate or accessory plagioclase, and a little magnetite or ilmenite. 

 Apatite has not been demonstrated in thin section. 



The nodules occur in the trachydolerite of the cinder-cones as 

 well as of the adjacent flows. In a few cases observed, the nodules 

 of the cinder-cones formed ellipsoidal bodies without any adhering 

 trachydolerite, as if each of these nodules represents a solid mass 

 exploded out of the vent and freed from liquid magma by the 



