Institution

)
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single bottom-sediment sample (Core KN25-4GPC, 548 em) with
hi gh montmori 11 oni te and mi xed-l ayer mi nera 1 content were
made, using different sample concentrations on each silver
filter. Concentrations of samples on ten filters ranged
from 0.025 mg/cm2 to 6.4 mg/cm2, and they were checked by
weighing similar aliquots filtered onto preweighed Nuclepore
filters (0.4 ~m pore size). The effect of particle size on
the analysis of each sample was assumed to be uniform since
all aliquots were taken from the same dispersed sediment
sample. Instrument conditions and x-ray procedures are
described in Chapter iv.
Fairly consistent mineralogical compositions were
observed at sample concentrations greater than about
1.6 mg/cm2 (7.28 ~m sample thickness; Table 7.1) using the
peaks and weighting factors of either Hathaway (1972a) or
Biscaye (1965). At lower sample concentrations, however,
there is a marked decrease in the calculated abundance of
montmorillonite and montmorillonite + mixed-layer material,
with a corresponding increase of illite. No basal
reflections are recorded in the x-ray diffraction pattern
202
below concentrations of about 0.1 mg/cm2 (0.22 ~m thickness).
The abundance of kaolinite and chlorite is quite
uni form when determi ned by ei ther method of cal cul ati on
where basal reflections (peaks) are well enough developed
to facilitate comparison. The exception is that these two
minerals appear to increase slightly in abundance at high