Chemical analyses of lunar surface materials were obtained in situ by Surveyors 5, 6, and 7. Mare samples were analyzed by Surveyors 5 and 6, which landed in Mare Tranquillitatis and Sinus Medii, respectively [Turkevich et al., 1967b, 1968]. The Surveyor-7 analyses were made in a terra region near the crater Tycho, which is thought to be covered with éjecta from that crater [Patterson et al., 1969]. The two adjacent samples in Mare Tranquillitatis were at least partially covered with material thrown out by the footpads of the spacecraft as it slid down the side of a small crater.