They dubbed the igneous survivors pristine rocks. The criteria for the recognition of igneous rocks include coarse-grained igneous textures, uniform mineral compositions, and low concentrations of siderophile elements such as iridium and silver (siderophile elements tend to concentrate in metallic iron), which were added to breccias by impacting projectiles rich in siderophile elements.

Petrologists subdivided the FAN suite into four subgroups, showing that the FAN suite is complicated, as were the processes than led to its formation. The subgroups are ferroan anorthosites (the most abundant, with a plagioclase composition of An>95), sodic anorthosites (An92–95), mafic ferroan rocks (plagioclase abundance is still high, typically >80%, with An>95), and mafic magnesian rocks (plagioclase abundance is >75%, with An>95). This range in composition suggests that the rocks formed at different stages of crystallization of a chemically complicated magma ocean. However, things may be even more complicated. Takeda et al. (2006) describe a chip of magnesian anorthosite in lunar meteorite Dhofar 489 (sample d2, Figs . 2 and 3). The sample has the same low concentrations of incompatible elements and low Na/Ca as the ferroan anorthosites but has a much higher Mg#.

Figure 4 Photomicrographs of pristine highland rocks and a granulite. (A) FAN sample 62236,5 is a plagioclase cumulate with intercumulus orthopyroxene (with augite exsolution lamellae). This area is particularly rich in pyroxene; plagioclase comprises 85% of the bulk sample. (B) Mg-suite troctolite with cumulate olivine and plagioclase; sample 76535. (C) Unbrecciated clast of Mg-suite norite; sample 76255,73. (D) KREEP basalt with a subophitic texture characteristic of crystallization in a basaltic lava flow; sample 15386. (E) Felsite, showing a graphic intergrowth of quartz and K-feldspar; sample 14321,1047. (F) Granulitic breccia consisting of an assemblage of very fine-grained plagioclase, olivine, and orthopyroxene crystals with a hornfelsic texture; sample 79215,71. Abbreviations: Plag: plagioclase; Opx: orthopyroxene; Pig: pigeonite; Qtz: quartz; Kspar: potassium feldspar.

The Mg-suite is enriched in KREEP compared to the ferroan anorthosite suite (Fig. 3). It thus has the unusual attribute of having high concentrations of trace elements coupled with relatively high Mg#. In other words, the major-element fractionation index suggests primitive magmas, but the trace elements indicate evolved magmas

While the thickness of the crust is uncertain, the high Al2O3 content of the highlands requires that the mantle contain no more than 1 wt% Al2O3 if the Moon is not enriched in refractory elements (Taylor et al. 2006). On the basis of geochemical signatures in some mare volcanic glasses, Neal (2001) postulated that the lunar mantle below ~500 km contains 2–3% garnet, which has implications for the bulk lunar Al2O3 content.