LUN-M - Mingled Mare and Highland Breccias
Synonyms: mingled lunar breccias, mingled breccias
General: This newly designed group has been recently proposed by the planetary scientists Randy Korotev and Anthony Irving at the 36th Lunar and Planentary Science Conference, in Houston, Texas. The members of the LUN M group consist of both, mare and anorthositic highland material.
Description: Most members of this group are regolith or fragmental breccias that resemble lunar regolith breccias of the LUN A group, dark grey rocks with an abundance of white clasts, and typical breccia-in-breccia textures. The colors of their fusion crusts is intermediate between lunar mare basalts, and anorthositic highland breccias, ranging from dull black to brown to olive-green.
Mineralogy: Being mingled breccias, the members of the LUN M group range from basalt-bearing anorthositic breccias to anorthosite-bearing basaltic breccias, differing in composition and mineral chemistry. Korotev and Irving have shown that these mingled breccias also show characteristic CaO/FeO, and Th/FeO ratios, resolving them clearly from the lunar highland anorthositic, and the lunar mare basalt fields.
Formation history: It is more than probable that most members of this group have their own, and rather special formation histories, and we can only give an example of such a formation history. Let's pick the first non-Antarctic lunaite, Calcalong Creek, as an example: It consists of approximately 50% highland anorthosite, 20% KREEP basalt, and 15% low-titanium mare basalt, together with other minerals that are typical of the lunar maria. Calcalong Creek can be regarded as a true transitional specimen between anorthositic highland regoliths and mare basalt regoliths. Recent research suggests that it probably formed between the lunar highlands and Oceanus Procellarum, one of the largest basaltic basins on the near side of the Moon.
Origin: Planetary. Comparisons to the lunar samples that have been returned by the Apollo and Luna missions have shown that the meteorites of this group are genuine samples of the Earth's satellite, the Moon. Have a look at our introductory section about the LUN group for further details. Different source craters have been identified, or proposed for some members of this rather heterogenous group, most of them located on the near side of the Moon.
Members: Five of the about eight members of this transitional group were recovered from the blue-ice fields of Antarctica, and aren't available to private collectors. Only two of the non-Antartic specimens get available on the private market, from time to time, at exorbitant prices. One is the famous Calcalong Creek from Australia, a 19g rock that has been recovered from a pile of Millbillilie eucrites by the "Meteorite Man", Robert Haag. The other sample is the recently classified NWA 3136, an anorthosite-bearing basaltic breccia from the deserts of Northwest Africa.