MAGMATIC DIFFERENTIATION IN HAWAII 



2 93 



morphic-granular to the diabasic. The thin-tabular plagioclase, 

 reaching i mm. in longest diameter, seems to be throughout the 

 basic labradorite, Ab 2 An 3 . The pale brownish augite has normal 

 habit, the major diameters reaching 0.8 or 1.0 mm. There is 

 nothing unusual about the minerals of this rock and further descrip- 

 tive details are superfluous. 



An analysis of the rock, by Mr. G. Steiger, gave the result shown 

 in col. 1 of Table I. 



TABLE I 



Si0 2 . . 

 Ti0 2 . 

 A1 2 3 . 

 Fe 2 3 . 

 Cr 2 3 . 

 FeO .. 

 MnO . 

 NiO .. 

 MgO . 

 CaO .. 

 Na 2 . 

 K 2 .. 

 H 2 0- 

 H 2 0+ 

 P 2 5 . . 

 C0 2 .. 

 S0 3 ... 

 BaO . . 

 SrO . . . 

 Zr0 2 . . 



Sp. gr. 



46.59 



None 

 None 

 None 

 None 

 None 



100.53 

 3.001 



I.; 



777 

 023 



075 

 014 

 001 



145 

 002 

 001 



545 

 132 

 022 

 003 



Calculated Norm of i . 



Orthoclase 1.67 



Albite n-53 



Anorthite 13 . 90 



Diopside 17.48 



Hypersthene 17.06 



Olivine 31.22 



Ilmenite 3. 50 



Magnetite 3.25 



Chromite 22 



Apatite 31 



Water 41 



JOO-SS 



1 Porphyritic gabbro of the Uwekahuna laccolith. 

 13 Molecular proportions in 1. 



2 Average analyses of three typical wehrlites. 



Using the chemical analysis and the Rosiwal optical method, 

 the minerals have been calculated to form the following weight 

 percentages : 



Olivine 40 . o 



Augite 31.0 



Labradorite ' 27.0 



Magnetite and ilmenite 1.7 



Apatite .3 



