A potpourri of pristine Moon rocks, including a VHK mare basalt and a unique, augite‐rich Apollo 17 anorthosite

Analysis of previously unstudied Apollo lithic fragments continues to yield surprising results. Among this year's samples is a small anorthosite fragment, 76504,18, the first pristine anorthosit e found from Apollo 17. This unique lithology strongly resembles the main type of Apollo anorthosites (ferroan anorthosites), but 76504, 18 has a far higher ratio (about 9) of high‐Ca pyroxene to low‐Ca pyroxene, higher Na in its plagioclase, higher contents of incompatible elements such as REE, and a higher Eu/Al ratio. Assuming that 76504, 18 is a cumulate with less than 45% trapped liquid, its parent melt probably had a negative Eu anomaly. In all these respects, 76504,18 seems more likely than (other) ferroan anorthosites to be closely related to typical mare basalts. Apparently this anorthosite was among the latest to form by plagioclase flotation above a primordial magmasphere; typical mare basalt source regions probably accumulated at about the same time or even earlier. Another previously unstudied fragment, 14181c, is a VHK (very high potassium) basalt that is similar in most respects to typical (“aluminous”) Apollo 14 mare basalt but has a K/La ratio of 1050. This lithology probably formed after a normal Apollo 14 mare basaltic melt partially assimilated granite. New data for siderophile elements in Apollo 12 mare basalts indicate that only the lowest of earlier data are trustworthy as being free of laboratory contamination.