Description and Identification of Soils (Visual-Manual Procedure) - Soil Properties: Testing, Measurement, and Evaluation - page 22

The American Society for Testing and Materials (ASTM) gives the
following definitions for various types of soil [1]:

DEFINITIONS

(1) For particles retained on a 3-in. (75-mm) US standard sieve, the
following definitions are suggested:

Cobbles —particles of rock that will pass a 12-in. (300-mm)
square opening and be retained on a 3-in. (75-mm) sieve, and

Boulders —particles of rock that will not pass a 12-in. (300-mm)
square opening.

(2) Clay —soil passing a No. 200 (75-µm) sieve that can be made to
exhibit plasticity (putty-like properties) within a range of water
contents and that exhibits considerable strength when air dry. For
classification, a clay is a fine-grained soil, or the fine-grained por-
tion of a soil, with a plasticity index equal to or greater than 4, and
the plot of plasticity index versus liquid limit falls on or above the
“A” line (see Figure 11-3).

(3) Gravel —particles of rock that will pass a 3-in. (75-mm) sieve
and be retained on a No. 4 (4.75-mm) sieve with the following
subdivisions:

coarse —passes a 3-in. (75-mm) sieve and is retained on a 3 ⁄ 4 -in.
(19-mm) sieve.
fine —passes a 3 ⁄ 4 -in. (19-mm) sieve and is retained on a No. 4
(4.75-mm) sieve.

(4) Organic clay —a clay with sufficient organic content to influ-
ence the soil properties. For classification, an organic clay is a soil
that would be classified as a clay, except that its liquid limit value
after oven drying is less than 75% of its liquid limit value before
oven drying.

(5) Organic silt —a silt with sufficient organic content to influence
the soil properties. For classification, an organic silt is a soil that
would be classified as a silt except that its liquid limit value after
oven drying is less than 75% of its liquid limit value before oven
drying.

(6) Peat —a soil comprised primarily of vegetable tissue in various
stages of decomposition, usually with an organic odor, a dark brown
to black color, a spongy consistency, and a texture ranging from
fibrous to amorphous.

(7) Sand —particles of rock that will pass a No. 4 (4.75-mm) sieve
and be retained on a No. 200 (75-µm) sieve with the following sub-
divisions:

coarse —passes a No. 4 (4.75-mm) sieve and is retained on a
No. 10 (2.00-mm) sieve.