Although some artificially produced sands may have small enough grains to appear homogeneous, beach sands are heterogeneous mixtures, according to Elmhurst College. Heterogeneous mixtures are composed of particles which vary in size, shape or phase.
Sand is mostly composed of tiny pieces of quartz, although other minerals, such as chalcedony, feldspar or magnetite, may be present as well. Sand only differs from materials such as silt and gravel by virtue of its size. If the grains are smaller than .05 millimeters, soil scientists classify the substance as silt. If the grains are larger than 2 millimeters, soil scientists consider it to be gravel.