Red desert sands are usually quartz coated with oxide of iron. Greensand deposits, found for the most part on the ocean floor, owe their color to glauconite, a potash-bearing mineral. Mixed with certain shore and river sands are grains of gold, platinum, and uranium and gemstones. Something of the history of sand can be learned by examining the texture of its grains under a microscope. The texture of sand can be described in terms of the size, angularity, shape, surface, and degree of sorting.
Grain size suggests the level of kinetic energy in the mediums that transport and deposit the sand.
The angularity or rounding of the grains can indicate the duration of abrasion by transport. Rounded sands have a long history of abrasion. They may have been subjected to wind action in deserts or along the shores of seas and lakes. Angular sands have either come from a nearby source or have been transported in a protective medium, such as mud flows. Another textural feature of sand is sand sorting, a measure of the range of grain sizes within a given deposit of sand.