* Heterogeneous mixtures have components that are not evenly distributed throughout the mixture. You can easily see the different parts of the mixture.
* Homogeneous mixtures have components that are evenly distributed, and you can't see the different parts.
In a mixture of pebbles and sand, you can clearly see the individual pebbles and the sand particles. They are not evenly distributed, and you could easily separate them (perhaps by size or by using a sieve).
