120 
about 13% MgCO.s. Determination of the 
amount of both of the calcite components, and 
of the aragonite component in the carbonate 
fraction of each sample, was made by comparing 
the peak ratios of these components prepared 
from known mixtures of the components (Gay- 
man, in preparation; Lowenstam, 1954). Al- 
though recognized corrections have not been 
made, it is thought that the relative quantitative 
results are significant. 
In all of the samples examined, with the ex- 
ception of one dune rock sample (40), the 
magnesium-rich calcite was much more abun- 
dant than the magnesium-poor calcite. This rock 
was obtained from a lithified relic dune which 
now forms a headland (sample station 40) of 
Kipu Kai Valley, south of Lihue. With this one 
exception, magnesium-poor calcite never consti- 
tuted more than 25% of the carbonate content 
of any sample. 
Magnesium-rich calcite was always present in 
the unconsolidated samples, and it was fre- 
Fig. 7. X-ray diffraction analysis of sample 60, 
showing the magnesium-rich and magnesium-poor 
peaks and the two aragonite peaks. The sample was 
taken in a water depth of 27 ft outside of Kapaa Reef 
(Fig. 8). 
PACIFIC SCIENCE, Vol. XVII, January 1963 
quently the only calcite component found. Mag- 
nesium-poor calcite was absent from the north 
and Napali coasts, and was abundant only in the 
dune rock and on the east coast in the vicinity 
of Kapaa Reef. The distribution of magnesium- 
poor calcite in the Kapaa area and the anomalous 
abundance of this component in the dune rock 
(sample 40) are discussed subsequently. 
According to Chave ( 1954^) , water tempera- 
ture and phylogenetic level are principle factors 
in determining the magnesium content of bi- 
ogenous calcite. High magnesium content is fa- 
vored by warmer water and lower phylogenetic 
level. Temperature has less effect on the mag- 
nesium content of the higher phylogenetic levels. , 
Blackman and Todd (1959) show magnesium 
content in foraminifera to vary with family. 
Heterostegina, one of the two common species 
of foraminifera in the samples, and two uniden- 
tified species of coralline algae taken from Ka- 
paa Reef, were X-rayed and found to contain j 
only magnesium-rich calcite. Conversely, Am- 
phistegina , the other common foraminifera, and 
a limpet were found to be composed mostly or ,i 
entirely of magnesium-poor calcite. 
Aragonite: Aragonite is generally consid- 
ered to be indicative of warm water deposition. 
It is deposited by three quantitatively significant j 
groups (Lowenstam, 1954): calcareous algae, j 
scleractinian corals, and molluscs. Samples from 
Kapaa Reef of two different species of coral [ 
( Acropora and a scleractinian coral) and one I 1 
specimen of gastropod (Conus) were X-rayed 
and found to be pure aragonite. One limpet, j 
mentioned previously, was found to be predom- 
inantly magnesium-poor calcite and only 28% 
aragonite. Although the aragonite in the car- , 
bonate fraction ranged from 19% to 45%, no 
systematic variation with depth or direction was | 
apparent. 
TERRIGENOUS: A cursory inspection of the 
differences in the terrigenous mineralogy was ' 
made by microscopic and X-ray diffraction tech- 
niques. A limited amount of X-ray data on the 
terrigenous components of the samples is pre- 
sented in Table 2 in the form of the olivine to 
feldspar peak height ratios. These data should I 
be regarded as only semiquantitative because i 
of the variation in peak height introduced by 
preferred orientation of the feldspar crystals. 
