Some important lunar science topics are not discussed in this booklet because they are not illustrated by the samples included in the provided sets. Moreover, many of the most important lunar rocks could not be used to make these sets of educational thin sections. However, the Apollo astronauts did collect several samples that were large enough for both scientific investigation and educational activity. From these, NASA has prepared 20 sets of thin sections (12 each) for use in petrology classes and an additional 201 encapsulated lunar disks (6 samples each) for use in secondary schools. The supplied samples necessarily differ slightly for each set; thus the general descriptions given in this booklet are only a guide to your own observations. For example, although it is not mentioned, you may find a big metal grain in your section. Furthermore, the photographs in this booklet may not be exactly like the thin section contained in your set.