What are the main characteristic of a heterogeneous mixture?
A heterogeneous mixture will contain substances that will not be uniformly distributed throughout the mixture.
In a heterogeneous mixture the concentration of one or more components will be higher in one area than in another.
If you dropped a handful of sand into a container, then added a handful of earth, and then a handful of pebbles, you would have a heterogeneous mixture.
The mixture would stay that way until you stir it until the visible differences between the materials fades out completely. Now you have a mixture that is less heterogeneous, and is approaching homogeneous (even distribution of components).