Chromitites in the late Archaean Fiskenaesset anorthosite complex are characterized by a most unusual mineral assemblage: highly calcic plagioclase, iron-rich aluminous chromites and primary amphibole. In particular, the chromite compositions are atypical of chromitites in layered igneous intrusions. However, rare occurrences of this mineral assemblage are found in modern arcs and it is proposed here that the late Archaean calcic anorthositic chromitites formed by the partial melting of unusually aluminous harzburgite in a mantle wedge above a subduction zone. This melting process produced a hydrous, aluminous basalt, which fractionated at depth in the crust to produce a variety of high-alumina basalt compositions, from which the anorthosite complex with its chromitite horizons formed as a cumulate within the continental crust. The principal trigger for the late precipitation of chromite is thought to have been the removal of Al from the basaltic melt through plagioclase crystallization, and the build-up of Cr through an absence of clinopyroxene. It is proposed that the aluminous mantle source of the parent magma was produced by the melting of a harzburgitic mantle refertilized by small-volume, aluminous slab melts. This process ceased at the end of the Archaean because the dominant mechanism of crust generation changed such that melt production shifted from the slab into the mantle wedge, thus explaining why highly calcic anorthosites are almost totally restricted to the Archaean.

The Grier(b), New Mexico meteorite, a single mass of 929.4 grams, was found in 1969. This brecciated chondrite can be classified as an L‐group from the bulk chemical analysis, ∼ 8 wt % metal with an estimated total iron content of 25 wt %, and the constant olivine (Fa25.5) and orthopyroxene (Fs23) compositions. The main portion of the meteorite fits the criteria for an L5 (grey to intermediate hypersthene) chondrite. A conspicuous, large (several cm3) dense fragment, texturally an L6–7 chondrite, contains practically no metal or chondrules. However, there is little variation in the bulk silicate and individual phase compositions between the fragment and the matrix. In spite of this, it seems unlikely that the fragment was created in situ because metal and sulfide are not found in the fragment‐matrix contact zone; thus the formation of olivines and pyroxenes in both parts, as well as the “draining” of metal from the fragment, occurred prior to accretion with little, if any, subsequent thermal metamorphism.

Madiun is a white, veined olivine-hypersthene, L6 chondrite. It can be classed as such on the basis ofits petrography and chemistry, uniform olivine (Fa24.2) and pyroxene (Fs 2 1.2) and total iron content of23.7 wt % Fe.