Page 43 - Petrophysics

PROPERTIES OF SEDIMENTARY PARTICLES 17

TABLE 1.7
STANDARD SIZE CLASSES OF SEDIMENTS

Limiting Parliclr Diameter
(mml (+uni~sl Size Class
2048 -
I024 -

256 -
512-
128-
64 -
32 -

16-
8-
4-
2-
‘4 -
I-
14 -
I/( -
‘/I6 -
I/= -
‘164 -
-
h a
‘/OS6 -
‘1512 -

The phi-size classification of Table 1.7 is based on a geometric scale
in which the size of adjacent orders differs by a multiple of two. The
phi-scale is used as a convenient scale for graphical presentations of
particle size distributions since it allows plotting on standard arithmetic
graph paper. It is based on the negative base-2 logarithm of the particle
diameter (d):

The size distribution may be represented as the cumulative curve of grains
that are retained on a given sieve size “percent larger,” or the grains that
pass through a given sieve, “percent finer.” The cumulative curve is often
represented as a histogram, which is more amenable to visual inspection.
Figures 1.3 and 1.4 compare the cumulative curves and histograms of
the Berea sandstone outcrop from Amherst, Ohio, to the coarse-grained