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PACIFIC SCIENCE, VoL XIII, July 1959 
Fig. 1. Samples of gibbsite amygdules from Haiku bauxite area east of Pauwela, Maui. Samples on the right 
show outer skin of amygdule, some of which are hollow in the center. 
Samples of the weathered rock containing 
the amygdules were collected to determine 
their chemical and mineral compositions. The 
amygdules were separated by dry-screening 
on a 20-mesh sieve and then any adhering 
matrix was removed by washing with distilled 
water. The samples of matrix and amygdules 
were dried and weighed. The chemical analy- 
sis of the samples of matrix and amygdules 
was made by procedures described by Piper 
(1944). The identification of the minerals in 
both the matrix and the amygdules was made 
by differential thermal analysis procedures 
proposed by Norton (1939). The samples 
were ground to pass through a 100-mesh 
sieve before analysis. 
The chemical composition of the amyg- 
dules and their respective matrices is pre- 
sented in Table 1. The samples of amygdules 
have a very uniform chemical composition 
which averages as follows: 1.6 per cent Si02; 
61.7 per cent AI2O3; 5.8 per cent Fe203; 
0.8 per cent Ti02; and, a loss on ignition of 
30.9 per cent. The chemical composition of 
the amygdules approaches that of the mineral 
gibbsite, the trihydrate of aluminum oxide. 
The theoretical analysis of gibbsite is approx- 
imately 66 per cent AI2O3 and a loss on igni- 
tion of 34 per cent. The average composition 
of the matrix is as follows: 2.5 per cent Si02; 
27.9 per cent AI2O3; 44.0 per cent Fe203; 9-6 
per cent Ti02; and a loss of ignition of 15.0 
per cent. The variation in chemical analysis 
of the samples of amygdules and matrix is 
