What is Sand

Sand means different things to different
people. A genteral, non-technical
dictionary definition for sand is "loose
particles of hard broken rock". More
restrictive definitions als exist which
depend upon the frame of reference or
academic discipline to which the
meaning of sand is to be applied. For
example, to a sedimentologist sand is
an unconsolidated (loose), rounded to
angular rock fragment or minteral grain
having a diameter in the range of 1/16 to
2 mm (0.0025 to 0.08 in.). An engineer
on the other hand may restrict the
meaning of sand to include only
rounded framents having a diameter of
0.074 mm (retained on U.S. standard

sieve no. 200) to 4.76 mm (passing U.S. standard sieve no. 4). Practically, sand
may be considered to consist of small detrital fragments (rock or minteral
particles liberated by mechanical disintegration of parent rock material), biogenic
particles (shells or shell fragments) or chemical precipitates (evaporites or
oolites) occurring in nature and distinguishable by the naked eye.

A sand sample can be described in terms of grain size, color, composition,
morphology (angularity and shape) and surface texture. Grain size is a result of
several factors, including composition, durability, severity of weathering
conditions, transport distance from its site of origin, and physical sorting by wind
and/or water currents.

A variety of scales exist for measuring grain size. One which nearly all sand
collectors use, and the easiest to remember, is the "Wentworth Article Size
Classification for Sand", which uses a geometric interval of 1/2 to define the
limits of each size fraction. In descending order, the Wentworth sand
classification scheme is as follows:

Size limits of sand grains and other particulate material.

A population of sand grains examined at low magnification is often not uniform
as revealed by the occurrence of a mixture of grain colors, morphologies and
sizes. Whenever a wide range of grain sizes occurs withins a sample, the
sample is regarded as being "very poorly sorted." If there exists a very limited
variation in grain size within a population, the sample may be described as "very
well sorted." those samples have sorting characteristics between the extremes
will be graded as well sorted, moderately sorted or poorly sorted depending on
the range and relative percentages of grain size fractions.

Degree of angularity, also referred to as roundness, is a property that reflects the
formative processes (weathering, transport, abrasion and deposition) involved in
forming a sand deposit. Generally speaking, the more well rounded the individual
grain, the greater the energy involved in transport or the longer the duration of
transport. Sand grains in beach environments are subjected to high-energy
abrasion involving collisions with numberous other grains due to the action of
waves. Aeolian (eolian is an appropriate alternative spelling), are wind
transported sands also commonly well rounded by high energy collisions and
abrasion. Particles transported long distances by rivers or streams may also
achieve a high level of roundedness. Variations in the durability of different
mineral types also affect rounding.

Rounded particles may also form by precipitation in near shore ocean currents.
Ooliths are rounded grains formed by concentric precipitation of calcium
carbonate around a pre-existing particle such as a small shell fragment or quartz
grain that acts as a site of nucleation. They commonly form in areas where
strong bottom currents exist, such as tidal channels or near shore sites where
strong currents exist.

Degree of rounding or angularity defines one aspect of the shape of a sand
particle. A more complete characterization of particle shape requires
consideration of the way size differs (or remains the same) according to direction
within individual grains. Particles, which are tabular or shaped like a disk, are
said to be oblate. Equdimensional particles are called equant. Elongated and
somewhat flattened particles are bladed. Rod--shaped particles are prolate.

Surface texture refers to small-scale features of a sand grain's surface which have
no apparent bearing on its overall shape. Examples of surface textures include
polished and frosted. A polished texture is commonly observed on grains which
have been transported by water, and correspondingly are typically rounded.
Frosting is produced by collision with other sand grains and is commonly
observed in aeolian sands.