A homogeneous mixture that does not settle out upon standing is, by definition, a suspension. The particles in the mixture are suspended throughout the entire volume of fluid.
In this blog post, we will explore why some liquids have a tendency to form suspensions and others do not. In order for a suspension to form, the particles in the mixture must be much smaller than those of its solvent.
In addition, they also need to be insoluble and have different densities than their surrounding fluid. If these conditions are met then when you shake up a liquid it will quickly settle out into two layers:
One consisting mainly of small particle solids at one end and another consisting mainly of clear solution on the other side with only some suspended particles floating in between them.
The difference in density is what causes gravity-driven settling rather than any type of chemical reaction that might occur inside the bulk volume where there is no agitation provided by shaking or stirring.