A suspension is a heterogeneous mixture that has particles held in a liquid or gas that are not dissolved, such as sand in water, oil in water and smoke in air. The key characteristic that differentiates a suspension mixture from a solution mixture is the heterogeneous property of a suspension, versus the homogeneous property of a solution. This means that the components in a suspension mixture do not bond together to create one uniform mixture.
This property helps to identify a suspension. If the components separate when left alone, the mixture is a suspension. For example, cleaning a shelf disperses dust into the air, creating a mixture, but eventually the dust settles. Dust in air is a heterogeneous suspension mixture.
The classification of suspension mixtures involves particles larger than those of other types of heterogeneous mixtures. These larger particles lend suspension mixtures some other identifiable properties. Suspensions are murky or opaque in appearance and do not transmit light. Muddy water is a suspension that easily shows these characteristics. Dirt is dispersed but not dissolved in water, causing the mixture to become murky and unable to transmit light. If left alone, the dirt eventually settles, proving that it is a suspension mixture.