Suspensions are mixtures of two different substances, one of which consists of small particles that eventually settle down as sediments. These particles are usually larger than one micrometer. Suspensions are found in nature in the form of mud, sand in water, or dust, soot and sea salt in air.
Suspensions are different from colloids, which contain smaller particles, and solutions, in which the solute does not exist as a separate substance and is homogeneously mixed with the solvent. Colloids are also typically stable and do not separate due to sedimentation. Both suspensions and colloids can consist of substances in any states of matter, such as liquids and solids mixed into gases, or gases, liquids and solids dispersed into other liquids and solids.