Chapter 9: Theory and processes relating to the lunar maria from the surveyor experiments

Prior to the Surveyor missions, there were three principal theories about the chemical constitution of the lunar maria: that the maria were (1) chondritic, (2) basaltic, or (3) silicic. Three types of materials recovered on Earth were suspected of coming from the maria: (1) chondritic meteorites, (2) basaltic achondrites, and (3) tektites.
The Surveyor chemists have now spoken: Turkevich, Franzgrote, and Patterson find that, in Mare Tranquillitatis (ref. 9-1) and Sinus Medii (see ch. 7 of this report), the composition is basaltic. It is unmistakably too poor in magnesium to be like either kind of chondritic meteorite. It is too rich in the heavier elements, iron and calcium, to resemble terrestrial silicic rocks (the granitic kindred) or tektites.