Littoral Sedimentary Processes — I nman, Gayman and Cox 
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MEDIAN DIAMETER, MICRONS 
62 125 250 500 1000 
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MEDIAN DIAMETER, PHI UNITS 
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JRM 
Fig. 6. Relation between beach slope and sand size. 
Exposed beaches generally have lower slopes than pro- 
tected beaches. 
opercula, pelecypod valves, and bryozoan frag- 
ments, made up less than 5% of the samples. 
Most of the remaining nonterrigenous compo- 
nent of the sand consisted of rounded calcareous 
grains, sometimes etched, pitted, or stained. 
A rough count indicated that Amphistegina 
and Heterostegina accounted for up to 20% of 
the grains in some of the samples. Since these 
foraminifera occurred most commonly in the 
size range of 500 to 1500 microns, they were 
more abundant in the coarser sediments. Am- 
phistegina were most common in the finer half 
of this range. 
Several indentifiable skeletal or shell frag- 
ments, collected from the reefs and beaches of 
Kauai, or in one case from Oahu, were examined 
by X-ray diffraction. The results and a review 
of the literature suggest that, in this area, the 
aragonite is secreted principally by corals and 
molluscs; the magnesium-rich calcite by forami- 
nifera, coralline algae, and echinoids; and the 
magnesium-poor calcite by molluscs and by Am- 
phistegina madagascariensis. 
Chemical and Mineralogical Analysis 
All of the sand samples were examined quali- 
tatively, and representative samples were also 
examined quantitatively to determine the chemi- 
cal, mineralogical, and biological composition. 
The carbonate content of all of the samples was 
determined to an accuracy of about 1%, using a 
gasometric technique described by Bien ( 1952 ) . 
Mineralogical determinations were made with a 
petrographic microscope and by X-ray diffrac- 
tion, using a North American Phillips Diffrac- 
tometer. 
TOTAL CARBONATE: The total carbonate con- 
tent varied from 0.5%, in the river bottom sam- 
ples, to 95% in some beach samples. Fifty-two 
of the samples had carbonate contents greater 
than 80%, while only 17 contained less than 
50% CaC0 3 . Although high carbonate values 
occurred on all coasts, samples from the east 
coast were composed almost entirely of bioge- 
nous material. The sands showing the highest 
carbonate values on the north, south, and Mana 
coasts were taken from those beaches which 
were most distant from large streams (Table 2). 
On the east (windward) coast and on the east- 
ern part of the north coast, the presence of large 
streams appeared to have little effect on the car- 
bonate content of the beach sediments. Low car- 
bonate values were typical of the beaches west 
of the Waimea River mouth on the south coast 
between sample stations 15 and 25 and, to a 
lesser degree, in Hanalei Bay on the north coast. 
CALCITE: The X-ray patterns of the sand sam- 
ples showed that the calcite frequently consisted 
of two components, magnesium-rich and mag- 
nesium-poor calcite (Fig. 7). A quantitative de- 
termination of the amount of magnesium car- 
bonate in each of the calcite components (i.e., 
the mineral species of the component) was made 
by comparing the peak location of each com- 
ponent with the curve published by Goldsmith 
et al. (1955: fig. 1). In the Kauai samples, the 
magnesium-poor peak represents a calcite con- 
taining from 2% to 3% MgC0 3 ; the magne- 
sium-rich peak represents a calcite containing 
