A change in the gene pool of a population form one generation to the next that does not necessarily result in speciation is an example of

Genetic Drift

Explanation:

Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance or sampling error.  Genetic drift occurs in all populations of non-infinite size, but its effects are strongest in small populations.  This process may result in the loss of some alleles (including beneficial ones) and the fixation, or rise to 100% frequency, of other alleles.  It also have major effects when a population is sharply reduced in size by a natural disaster (bottleneck effect) or when a small group splits off from the main population to found a colony (founder effect).

the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.