294 
and amygdules of gibbsite depends upon wet 
and dry conditions to provide the means of 
movement of the alumina in order to produce 
the rhythmic precipitation which is so char- 
acteristic of their structure. 
SUMMARY 
The occurrence of gibbsite amygdules in a 
bauxite deposit of the Haiku area of Maui 
has been described. The amygdules are 
formed by the rhythmic precipitation of hy- 
drated aluminum oxide in cavities which are 
relics of the parent rock. These cavities were 
probably gas bubbles in the original lava. The 
amygdules contain approximately 62 per cent 
AI2O3, 6 per cent Fe203, and trace amounts 
of silica and titania. The hydrated aluminum 
oxide has been identified as gibbsite by dif- 
ferential thermal procedures. 
PACIFIC SCIENCE, Vol. XIII, July 1959 
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Fellom, Roy. 1957. Hawaii bauxite. Light 
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Norton, F. H. 1939. Hydrothermal forma- 
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