Scientists say that clastic sediments are well-sorted when the individual grains are all about the same size. When big chunks and tiny grains are mixed together, the sediments are considered poorly sorted. In general, the distribution of size of the particles in a clastic sedimentary rock may indicate how fast the water or wind transported the grains before they were deposited and ultimately became cemented into rock. The faster the flow, the larger the particles it can push. In some cases, unusually dense particles, such as nuggets of gold or magnetite, drop to the bottom of a stream or river sooner than similarly sized grains of lighter minerals. Also, after a lengthy period of movement through turbulent water, less resistant particles wear down or disintegrate altogether, leaving the more durable mineral grains behind. All these clues help geologists figure out the stories behind these fascinating rocks.